Mobilization of T lymphocytes following cardiac transplantation. Evidence that CD4-positive cells are required for cytotoxic T lymphocyte activation, inflammatory endothelial development, graft infiltration, and acute allograft rejection.

Modified limiting dilution analysis (LDA) techniques were used to evaluate the mobilization of antigen-stimulated helper T lymphocytes (HTL) and cytotoxic T lymphocytes (CTL) following allogeneic heterotopic cardiac transplantation. These modified LDA techniques allow a quantitative comparison of T cells that have been stimulated by antigen in vivo versus unstimulated precursor T cells of the same antigen specificity. Endothelial changes associated with mononuclear cell infiltration of the transplant were studied using endothelia-specific monoclonal antibodies and immunohistochemistry. Early (day 3) infiltration of cardiac allografts was characterized by a prevalence of donor alloantigen-specific HTL over CTL. Immunohistology revealed that the day-3 infiltrate was associated with areas of differentiated vascular endothelium, located primarily in the subepicardial region. Though donor-specific precursor HTL and CTL were present in the peripheral lymphoid tissues and blood, very few of them had been stimulated at this early time. During the latter phases of the response (days 6-9), antigen-stimulated HTL and CTL were present in the rejecting heart with CTL dominating the response. Accumulation of large numbers of donor-specific CTL in the allograft correlated with extensive inflammatory endothelial development, myocyte destruction, and loss of graft function by day 9. Stimulated HTL and CTL were detectable in peripheral lymphoid tissues at days 6 and 9. In addition, a marked increase in the number of donor-specific precursor CTL, but not precursor HTL, was observed in the lymphoid tissues at the peak of the response. Depletion of class II MHC-restricted T cells by in vivo treatment with anti-CD4 mAb eliminated HTL activity in all lymphoid compartments assessed and markedly reduced the number of CTL infiltrating the allograft. In addition, no stimulated CTL were detectable in lymphoid tissues, and the number of precursor CTL was not increased. In anti-CD4-treated recipients, cardiac allografts remained functional with minimal histological evidence of rejection for at least 21 days. Though graft-associated inflammatory endothelia were absent in anti-CD4-treated recipients at day 6, endothelial differentiation was observed in day 21 allografts in anti-CD4-treated recipients. These observations indicate that inflammatory endothelial development may precede T cell infiltration and subsequent loss of the cardiac allograft function. Thus, CD4-positive HTL are required for (1) graft-associated inflammatory endothelial development; (2) CTL activation in peripheral lymphoid tissues; (3) CTL accumulation in allografted tissues; and (4) acute cardiac allograft rejection.     

Frequency of human alloantigen-reactive T lymphocytes. II. Method for limiting dilution analysis of alloantigen-reactive helper T cells in human peripheral blood

Quantitative immunologic techniques for analysis of human alloreactivity are currently lacking in transplantation immunology. We report a rapid, sensitive, and quantitative limiting dilution analysis technique that provides a minimal estimate of the number of peripheral blood mononuclear cells (PBMC) capable of secreting interleukin-2 (operationally defined as helpter T lymphocytes) when cultured in vitro with allogeneic PBMC bearing serologically identified MHC disparities. Using this LDA technique, we have estimated that approximately 1/500 to 1/2000 (0.2% to 0.05%) of the PBMC from various individuals can secrete IL-2 after in vitro contact with completely major-histocompatibility-complex-disparate PBMC. Under normal conditions the HTL frequency in human peripheral blood appears quite stable, based on serial analysis of HTL frequency in a healthy human donor. This LDA technique is more rapid and informative than the MLR, and may be useful for pretransplant evaluation and posttransplant monitoring of donor reactivity in transplant recipients.     

Development and evaluation of a limiting dilution analysis technique that can discriminate in vivo alloactivated cytotoxic T lymphocytes from their naive CTL precursors

We describe a permutation of the conventional limiting dilution analysis (LDA) technique that allows, for the 1st time, the differential enumeration of alloantigen-specific CTL that have been activated by alloantigens in vivo. This technique does not detect nonactivated CTL precursors, even those with similar alloantigen specificity. Data are presented to validate this limiting dilution analysis technique. Using this LDA technique, we demonstrate that large numbers of the donor-reactive CTL arrive in sponge matrix allografts (f = 1/3,599 cells), most or all of which are in an activated state (f = 1/4,385 cells). In contrast, alloactivated CTL constitute only a small fraction (f = 1/57,208 cells) of the donor-reactive CTL in the regional lymph node (f = 1/1,873 cells) of the same sponge allograft recipients. As expected, regional lymph nodes from sponge isograft recipients contain DBA/2-reactive CTL precursors (f = 1/1,873 cells), but no activated DBA/2-reactive CTL (f less than 1/385,529 cells). This LDA technique should be useful in studies regarding activation and redistribution of alloreactive CTL caused by allograft implantation.     

Study of murine T cell migration using the Thy-1 allotypic marker. Demonstration of antigen-specific homing to lymph node germinal centers

We describe the use of Thy-1 alloantigen as a marker for in vivo T lymphocyte homing studies. Following transfer of 5 x 10(7) peripheral node T cells i.v., 32% of the transferred cells could be recovered in the host lymphoid organs (spleen, lymph nodes, Peyer's patches, and thymus); 11% of the T cells in the lymph nodes were donor derived. The transferred T cells assume the same microenvironmental and immunophenotypic distribution as the host T cells. The transferred T cells are identifiable in peripheral lymph nodes up to 170 days posttransfer, gradually declining in number during this time without evidence of rejection. This Thy-1 transfer technique permits T lymphocyte homing studies to be performed under physiologic conditions without problems of loss of lymphocyte subsets, selective labeling of lymphocyte populations, or long-term marker loss or dilution. We then employ this technique to demonstrate the antigen-directed homing of peripheral T cells to lymph node germinal centers.     

Comparative analysis of in vivo T cell depletion with radiotherapy, combination chemotherapy, and the monoclonal antibody Campath-1G, using limiting dilution methodology

We have investigated the efficacy of standard conditioning regimens for bone marrow transplantation in depleting functional T lymphocytes in vivo and have compared it with the efficacy of the monoclonal antibody Campath-1G. Using limiting dilution techniques the frequencies of proliferating T cell precursors (PTL), cytotoxic T cell precursors (CTL-p), helper T cell precursors (HTL-p), and mature helper T cells (HTL) were determined before and after treatment. Both total body irradiation and combination chemotherapy with busulfan/cyclophosphamide were highly efficient at depleting PTL, CTL-p, and HTL-p (0-4 days) but spared HTL to a variable extent (0-99.5%). In the majority of patients treated with Campath-1G a similar degree of PTL, CTL-p, and HTL-p depletion was achieved, and, in addition, HTL were effectively removed (greater than 95.5%). These results suggest that Campath-1G could be successfully employed in depleting radio- and chemotherapy-resistant host T lymphocytes prior to T-depleted bone marrow transplantation.     

In vivo mechanisms of alloreactivity. II. Allospecificity of cytotoxic T lymphocytes in sponge matrix allografts as determined by limiting dilution analysis

We have examined the frequency and alloantigen specificity of CTL that accumulate in sponge allografts (sponges seeded with allogeneic splenocytes) in sponge isografts (sponges seeded with syngeneic splenocytes), and in splenocyte-free sponge implants. Using limiting dilution analysis (LDA), we observed that sponge isografts and splenocyte-free sponge implants from C57BL/6 (H-2b) mice usually acquire small numbers of CTL (less than 250 cells per graft) with DBA/2 (H-2d)-reactivity or C3H/HeJ (H-2k)-reactivity. These alloreactive CTL are not detectable in conventional 51Cr-release assays, presumably because they are too infrequent and/or because they are inactive CTL precursors. When we examined the accumulation of alloreactive CTL in sponge allografts, we observed that DBA/2 sponge allografts from C57BL/6 recipients accumulate 10 to 100 times more DBA/2-reactive CTL than alloantigen-free sponge grafts. Nonetheless, these donor-reactive CTL rarely constitute more than 0.5% of the T cells recovered from sponge allografts, even at the peak of the rejection response. This raises questions concerning the remaining 99.5% of the allograft-infiltrating T cells. We were unable to detect by LDA any host-reactive CTL in sponge allografts, thus excluding the possibility that some of the remaining T cells were host-reactive CTL of donor origin which diluted graft-reactive T cells. However, using LDA we did detect a significant number of third-party (C3H/HeJ)-reactive CTL in sponge allografts, suggesting that the intense immune response at a graft site might facilitate indiscriminate recruitment of T lymphocytes. Alternatively, this enhanced third-party alloreactivity might reflect the proliferation of donor-reactive CTL with incidental crossreactivity for C3H/HeJ alloantigens. While testing these two alternatives, we observed that LDA cultures designed to detect third-party-reactive CTL could also support the growth of the in vivo-activated, donor-reactive CTL from sponge allografts; This compromised enumeration by LDA of the less frequent, third-party-reactive CTL by LDA. Although LDA is the only method that detects the growing population of third-party-reactive CTL in sponge allografts, technical restraints exclude LDA as a method of determining whether donor-reactive CTL and third-party-reactive CTL are separate or overlapping CTL subpopulations. Hence, it remains unclear if third-party-reactive CTL are a significant or insignificant proportion of the CTL that infiltrate sponge allografts.(ABSTRACT TRUNCATED AT 400 WORDS)     

Detection of alloreactive T cells by flow cytometry: a new test compared with limiting dilution assay

BACKGROUND: Frequencies of alloreactive T cells determined by limiting dilution assays (LDA) may not adequately reflect the donor-reactive immune status in transplant recipients. To reevaluate LDA frequencies, we developed a flow cytometry test for direct determination of alloreactive T-cell frequencies and compared these frequencies with classical LDA estimates of frequencies. METHODS: For determination of frequencies by flow cytometry, peripheral blood lymphocytes (or lymphocytes taken from primary mixed lymphocyte culture) were stimulated with either Epstein-Barr virus-transformed lymphoblastoid cell lines or T cell-depleted spleen cells and stained for intracellular interferon (IFN)-gamma production and CD69. In lung transplant recipients, frequencies of IFN+ alloreactive T cells were compared with LDA frequencies, that is, cytotoxic T lymphocyte precursors and helper T lymphocyte precursors. RESULTS: With flow cytometry, alloreactive T cells were detected after overnight allostimulation as IFN-gamma CD69bright cells (range, 0.1-0.58% and 0.1-0.66% of total CD4 and CD8 cells, respectively). Frequencies increased 25-fold or more when lymphocytes were prestimulated in primary mixed lymphocyte culture before testing. After lung transplantation, mean donor-specific IFN+ CD8 T-cell frequencies did not decrease as mean donor-specific LDA cytotoxic T lymphocyte precursor frequencies, whereas no difference was seen in pretransplantation samples or third-party-specific frequencies at both time points. Mean frequencies of IFN+ CD4 did not differ from helper T lymphocyte precursors at both time points, but frequencies did not correlate. CONCLUSIONS: The flow cytometry test allows a direct measurement of alloreactive T-cell frequencies and demonstrates a discrepancy between donor-specific IFN+ CD8 T-cell frequencies and LDA CLTp after transplantation. This may be a result of the existence of "functional diverse" alloreactive T cells or of activation-induced cell death of donor-reactive T cells during long (LDA) culturing, which is avoided in the flow cytometry test.     

EBV-B cells as antigen presenting cells in characterization of the self/donor context of allorecognition by T lymphocytes

Alloreactivity is caused by T cell recognition of foreign histocompatibility antigens according to two models: (i) indirect recognition, in which processed allogeneic antigens are presented by self-major histocompatibility complexes like any other foreign antigen, and (ii) direct recognition, where the foreign MHC itself is recognized breaking the T cell recognition rule of self-restriction. This paper uses these two cases of alloantigen presentation as illustrative examples to investigate (i) the capacity of Epstein-Barr virus-transformed B cells (EBV-B cells) to process alloantigens, and (ii) in vitro assays with EBV-B cell lysate as a source of alloantigen, in order to characterize alloreactive T cell populations. A microculture system was established using donor EBV-B cell lysate as a source of the allogeneic antigen and donor or recipient EBV-B cells as antigen presenting cells to investigate whether alloantigen is recognized by effector T cells from the recipient. T lymphocytes produced after expansion in the presence of interleukin-2 from four samples of liver biopsies (three patients) and four samples of bronchoalveolar lavages (four patients) were used as effector cells. Upon human leucocyte antigen class II typing, these expressed the patient phenotype. When the T lymphocytes were from liver grafts, the recognition involved donor antigens presented by donor EBV-B cells (direct recognition). On the other hand, when the T lymphocytes were cultured from lung grafts, they mainly recognized antigens of donor EBV-B cell lysates in a self-restricted context (indirect recognition). These data suggest that EBV-B cells can provide allogeneic determinants recognized by T cells in donor or self-contexts, i.e. through either direct or indirect recognition.     

Mediation of skin allograft rejection in scid mice by CD4+ and CD8+ T cells.

We analyzed the role of CD4+ and CD8+ T cells in H-2-disparate skin allograft rejection in the mutant mouse strain C.B-17/Icr scid with severe combined immunodeficiency. On the day of skin allografting, scid mice were adoptively transferred with negatively selected CD4+ or CD8+ splenocytes from normal unsensitized C.B-17/Icr mice. These populations were obtained using a double-mAb--plus--complement elimination protocol using anti-CD4 or anti-CD8 mAb that resulted in no detectable CD4+ or CD8+ cells by FACS and negligible numbers of cytolytic T lymphocytes by limiting dilution analysis in anti-CD8 treated populations. Spleen cells were removed from grafted mice at the time of rejection and were tested in vitro for antidonor reactivity in several assays: mixed lymphocyte culture, cell-mediated lympholysis, and LDA for CTL and for IL-2-producing HTL. The presence of Thy 1.2+, CD4+, or CD8+ cells was determined by FACS. All control C.B-17 mice and scid mice adoptively transferred with nondepleted CD4+, and CD8+ cells rejected skin allografts with similar mean survival times (15.6 +/- 1.5, 18.8 +/- 3.4, 18.0 +/- 5.4, respectively), whereas control scid mice retain skin allografts indefinitely (all greater than 100 days). C.B-17 syngeneic grafts survived indefinitely in all groups. At the time of rejection, splenocytes from scid mice receiving CD4+ cells had negligible donor-specific cytotoxicity in CML and negligible numbers of CTL by LDA, but demonstrated a good proliferative response in MLC and IL-2-producing cells by LDA (frequency = 1/1764). There were no detectable CD8+ cells present by FACS analysis. Conversely, splenocytes from scid mice adoptively transferred with CD8+ cells had strong donor-specific cytotoxicity in CML (58.8% +/- 16.1%) and CTL by LDA (frequency = 1/3448), but no significant proliferation was detected in MLC. There were no detectable CD4+ cells by FACS, but there were small numbers of IL-2-producing cells by LDA (frequency = 1/10,204). These data demonstrate that CD4+ cells adoptively transferred into scid mice are capable of mediating skin allograft rejection in the absence of any detectable CD8+ cells or significant functional cytolytic activity. The adoptive transfer of CD8+ cells also results in skin allograft rejection in the absence of detectable CD4+ cells. The detection of small numbers of IL-2 secreting cells in these mice may indicate that CD(8+)-mediated allograft rejection in this model is dependent on IL-2-secreting CD8+ cells.     

Experimental studies on the mode of action of cyclosporine and FK506 assessed by proliferation response of human cloned T lymphocytes]

We applied cloned human T lymphocytes established in our laboratory to evaluate the mode of action of Cyclosporine (CsA) and FK506. Phenotypic and functional analysis led us to conclude that HTL403 was a helper T cell clone and HTL805 a cytotoxic one. Susceptibility of HTL-403 to the immunosuppressants demonstrated that alloantigen-driven proliferative response can recover to the rIL2-driven level by the addition of rIL2 at higher concentration of the agents. Although full recovery was not observed in FK506, this finding indicated that FK506 as well as CsA inhibit IL2 secretion from HTL403. FK506 showed remarkable suppressive effect on the proliferative response of HTL-805 even at a considerably low concentration, while CsA suppressed such a response dose-dependently. We concluded that FK506 can be used to reverse ongoing acute rejection as well as to prevent acute rejection.     

T cell depletion with anti-CD5 immunotoxin in histocompatible bone marrow transplantation. The correlation between residual CD5 negative T cells and subsequent graft-versus-host disease.

Twenty-nine patients with advanced leukemias (median age 34 years) received histocompatible sibling marrow that had been depleted of T cells by ex vivo incubation with anti-CD5 monoclonal antibody-ricin immunotoxin (T101-R) for the purpose of graft-versus-host disease prophylaxis. Donor cell engraftment was documented in 28/29 patients by DNA restriction fragment length polymorphisms. In this pilot study the dose of T101-R incubated with donor marrow was increased in a stepwise manner from 300 ng (10 patients) to 600 ng (5 patients) to 1000 ng immunotoxin (IT)/10(7) bone marrow mononuclear cells (14 patients) in an attempt to achieve more effective GvHD prophylaxis. A statistically significant reduction in acute GvHD was achieved for patients receiving marrow pretreated with 1000 ng of immunotoxin (34%) compared to recipients of BM treated with 300 ng immunotoxin (100%, P = 0.0004). T-depleted marrow samples were evaluated for residual T cell activity using several in vitro assays including proliferation to the purified mitogen PHA (HA-17) and in mixed lymphocyte culture (MLC), T cell cytotoxicity, a limiting dilution assay for detecting precursors of proliferating T cells (LDApPTL), and phenotypic analysis of viable T cells expanded in 16-day culture with interleukin 2. The extent of T cell depletion determined by LDA assay varied widely at each immunotoxin concentration used. Thus, there was no correlation between the dose of T cells infused and subsequent GvHD. Phenotyping of lymphocytes recovered from immunotoxin-treated marrow demonstrated that residual T cells were CD5 negative in all cases tested. The only in vitro parameter that predicted subsequent acute or chronic GvHD was the demonstration of viable CD5 negative lymphocytes with T cell phenotype (CD2, CD3, and/or CD7 positive) after 16-day culture with IL-2 of the T-depleted bone marrow. We observed that such CD5 negative cells expressing other T cell markers have cytotoxic function and speculate that these cells may be capable of mediating GvHD in allogeneic transplantation.     

Thromboxane augmentation of alloreactive T cell function.

Thromboxane (Tx) plays a vital role in the dysfunction and ultimate rejection of MHC-disparate renal allografts. In addition to its potent vasoconstrictory properties, in vivo studies have implied that Tx is capable of promoting immune cytotoxic T cell function within transplants. In this study, we have examined the in vitro effect of Tx inhibition on alloreactive immune cells using MHC-disparate mouse strain combinations. Coculture of either Tx-synthetase or Tx-receptor inhibitors modified the response of unprimed mouse lymphoid populations in a primary MLR, implying that Tx inhibition and not endoperoxide shunting was responsible for the modulatory effects seen. For example, B10.S lymphoid cells displayed decreased proliferation to H-2 disparate B10.A cells with Tx inhibitors present during the MLR, at pharmacologically active drug concentrations. Moreover, in vitro addition of TxA2 had an augmentory effect on the response in the primary and secondary MLR. Interleukin 2 production and percentages of T cell populations in the primary MLR were not affected by the presence of these compounds, although CD4 and CD8 expression was often increased in the treated populations. Finally, alloreactive primed effector cells also displayed reduced proliferation to specific alloantigen in a secondary MLR when Tx inhibitors were also present, although responses to IL-2 by T cells were not influenced by thromboxane inhibition. These data imply that thromboxane is an important immunoregulatory mediator capable of potentiating the function of naive and primed alloreactive immune T cell populations crucial to the rejection of the transplant.     

Dietary nucleotides, a requirement for helper/inducer T lymphocytes

Previous investigations have revealed that dietary nucleotide restriction delays the onset of primary murine cardiac allograft rejection and acute graft-versus-host disease followed H-2-incompatible bone marrow transplantation, suppresses sensitization to intradermally injected antigens and suppresses in vivo and in vitro lymphocyte proliferation to alloantigen or lectin stimulation. To determine the mechanisms responsible for these phenomena, BALB/c mice were placed on chow (F), nucleotide free (NF) diet, or NF diet supplemented with 0.25% RNA (NFR), with 0.6% adenine (NFA), or with 0.06% uracil (NFU). Following four weeks of dietary equilibrium, splenic lymphocytes harvested from naive or immunostimulated mice in the various dietary groups were stained with monoclonal antibodies directed Lyt 1, Lyt 2, 3, or surface mouse immunoglobulin (IgG) surface markers. While naive animals demonstrated no differences in lymphocyte subpopulations between groups, following complete Freund's adjuvant (CFA) stimulation, splenic lymphocytes for NF mice demonstrated 27.3 +/- 1.7% Lyt 1+ cells compared with F (32.6 +/- .04%) and NFR mice (33.2 +/- 1.2%) (P less than 0.02). Restriction of dietary nucleotides affected not only phenotypes of T lymphocytes, but also T cell function. Following conconavalin A stimulation of irradiated splenic lymphocytes, IL-2 production was decreased in NF mice compared with the F control group (P less than 0.01). The RNA-repleted diet maintained normal IL-2 production, while addition of adenine or uracil alone did not. Finally, NF diets adversely affected host resistance to the opportunistic pathogen Candida albicans. Following inoculation with 0.25 X 10(6) organisms NF or NFA-fed hosts succumbed more rapidly than F, NFR, or NFU fed hosts (P less than 0.001). These data suggest that helper/inducer T lymphocytes require exogenous nucleotides to respond normally following immune stimulation. Uracil may be the critical substrate, based upon the studies of Candida resistance. By understanding the metabolic basis of NFD-induced immunosuppression, the role of dietary nucleotides in combatting infection and alloantigen rejection can be more clearly defined.     

High frequency of IL‐4 producing helper T lymphocytes associated with a reduced incidence of heart allograft rejection

Abstract The reduction in the frequency of rejection episodes several months after heart transplantation (HTX) correlates with the development of donor‐specific nonresponsiveness. This is reflected in a reduced frequency of donor‐specific cytotoxic T cells (CTL) in the peripheral blood. We investigated whether the reduced CTL frequency and the incidence of rejection episodes coincided with a change in the frequency of either IL‐2‐ or IL‐4‐producing helper T lymphocytes (HTL). We measured the frequency of HTL before and at several time points after HTX in the blood of ten recipients, using limiting dilution analysis for IL‐2 and IL‐4. In most patients, HTL frequencies dropped immediately after transplantation, but returned to pre‐HTX values later after transplantation. No consistent decrease or increase in frequencies was observed long after HTX. In contrast to IL‐2, the HTL frequencies for IL‐4 before transplantation were significantly higher in patients without post‐HTX rejection episodes requiring treatment than in patients with such episodes. This phenomenon was observed for the in vitro responses towards both donor and third‐party cells. In conclusion, relatively high frequencies of IL‐4‐producing T cells may have a beneficial effect on the outcome of human heart transplantation, because they are associated with a reduced incidence of rejection episodes after transplantation.     

Selective deletion of antigen-specific, activated T cells by a humanized MAB to CD2 (MEDI-507) is mediated by NK cells

CD2 is a 50-kDa transmembrane glycoprotein that plays an important role in T and natural killer (NT) lymphocyte functions. CD2 serves as both an adhesion molecule and as a costimulatory molecule through interactions with its ligand, CD58, on antigen presenting or target cells. Consistent with earlier studies using a rat anti-CD2 mAb, we have shown that treatment of alloantigen stimulated T lymphocytes with a humanized mAb, MEDI-507 (IgG1, kappa), induced hyporesponsiveness to subsequent stimulation with alloantigen but not to mitogen (phytohemagglutinin). Fluorescence-activated cell sorting analysis of cells from mixed lymphocyte reaction (MLR) treated with MEDI-507 revealed pronounced deletion of T and NK cells, consistent with lack of proliferation in the MLR. MEDI-507 F(ab')2 fragments did not have inhibitory activity or induce deletion of lymphocytes in the MLR. Removal of the NK cell subset by magnetic bead depletion using anti-CD16 and anti-CD56 mAbs eliminated both the T cell deletion and the inhibitory effect. Reconstitution of NK depleted responder populations using autologous NK cells restored the MEDI-507-mediated deletion activity to levels measured in the original MLR. Formaldehyde-fixed NK cells failed to mediate the MEDI-507-induced deletion effect. Altogether, our studies indicate that activated T cells with MEDI-507 bound to CD2 are preferential targets for autologous NK cells through a nonapoptotic cytotoxic mechanism.     

Bryostatin/ionomycin-activated T cells mediate regression of established tumors

We have shown that adoptive transfer of tumor-sensitized lymphocytes activated in vitro with bryostatin-1 and ionomycin (B/I), and expanded in culture, can induce regression of small established tumors. We set out to determine whether similar treatment would be effective against larger tumors and what cells mediate this effect. We also attempted to shorten the ex vivo culture period with the ultimate aim of developing a more clinically useful protocol. BALB/c mice were injected in one footpad with IL-2-transfected 4T07 mammary tumor cells. Ten days later, popliteal draining lymph nodes (DLN) were harvested and activated with B/I for 18 h. Mice with either 3-day or 10-day 4T07 flank tumors were treated with cyclophosphamide (100 mg/ kg ip, CYP) alone or CYP followed the next day by infusion of either B/I-activated lymphocytes transferred immediately or activated cells that had been expanded in vitro for 3 or 10 days. In some experiments, mice were also treated with rat anti-mouse CD4 monoclonal antibody (GK1.5) or anti-CD8 antibody (2.43). All mice receiving CYP alone or CYP + sensitized, nonactivated DLN cells demonstrated progressive tumor growth. One hundred percent (6/6) of mice treated with CYP + AIT with B/I-activated,10-day expanded cells had complete regression of 3-day flank tumors. Treatment with activated, nonexpanded cells, induced tumor regression in a majority of mice, but was not as reliable as AIT with expanded cells. We developed a protocol with a shortened expansion period (3-day) that was efficacious for treatment of 4T07 when adoptively transferred to either 3 or 10 day tumor-bearing mice. In vivo depletion of CD4(+) cells had no effect on regression of 3-day tumors, but treatment with anti-CD8 antibody abrogated the effect of immunotherapy. Adoptive transfer of B/I-activated cells, with or without long-term expansion, induced regression of early and late stage 4T07 tumors and is dependent on CD8(+) but not CD4(+) T cells.     

The effect of cyclosporine on ornithine decarboxylase induction with mitogens, antigens, and lymphokines

Ornithine decarboxylase (ODC) is the initial enzyme in polyamine synthesis. An increase in ODC activity is associated with increased RNA, DNA, and protein synthesis. We have used the induction of ODC by mitogens and alloantigens in human peripheral blood lymphocytes as an intracellular marker of protein synthesis and lymphocyte activation. The immunosuppressive agent cyclosporine was found to inhibit both the mitogen and alloantigen stimulated induction of ODC in lymphocytes in a manner that parallels inhibition of subsequent 3H-thymidine incorporation. When purified T lymphocytes were stimulated with mitogen alone, minimal ODC activity was detected. The addition of 5% monocytes, human Interleukin-1 (IL-1), or T cell growth factor (IL-2) enhanced mitogen-induced ODC activity in T lymphocytes 4-10-fold. Cyclosporine inhibited the induction of ODC when T lymphocytes were combined with monocytes or growth factors. We conclude that (1) the induction of ODC in human lymphocytes by mitogen and alloantigen is inhibited in the presence of cyclosporine; (2) the induction of ODC activity in purified T lymphocytes requires the presence of both mitogen and monocytes or their products; (3) IL-1 and IL-2 can supplement for monocytes and augment the phytohemagglutinin induction of ODC in T lymphocytes; and (4) cyclosporine inhibits ODC induction in T lymphocytes stimulated with mitogen in the added presence of monocytes, IL-1, or IL-2. The inhibition of ODC induction and polyamine synthesis by cyclosporine adds insight into its mode of action on the mechanisms involved in early T cell activation.     

Alloantigen presentation by canine endothelial cells. Presentation of autologous alloantigens in vitro

Presentation of autologous alloantigen by certain cells in an allograft can result in allograft rejection. The precise type of cell in a graft responsible for this aspect of allograft rejection remains to be established. Here we report the capacity of canine venous endothelial cells to activate, in vitro, allogeneic lymphocytes for proliferation and differentiation by presentation of alloantigen. Antigen-presenting cell (APC)-depleted lymphocyte populations, prepared in a multistep procedure and tested for absence of APC, were cocultured with allogeneic venous endothelial cells. Proliferation and differentiation into cytotoxic T lymphocytes were measured. While mixed lymphocyte culture of APC-depleted lymphocytes did not result in proliferation and differentiation, coculture of allogeneic APC-depleted lymphocytes with venous endothelial cells resulted in proliferation and generation of cell-mediated cytotoxicity in these cultures. It is concluded that canine venous endothelial cells in vitro have the capacity to present alloantigen. The data suggest an essential role for endothelium in the initial phase of allograft rejection.     

Identification and characterization of the antigen-specific subpopulation of alloreactive CD4+ T cells in vitro and in vivo

We report the identification and characterization of the small subpopulation of alloantigen-specific T cells in vitro and in vivo. This subpopulation of T cells was distinguished by up-regulation of cell surface CD4 expression. These CD4high T cells were alloantigen specific in proliferation assays in vitro, and they expressed memory/activation markers, including CD44high and CD69high. Further studies demonstrated that these allospecific CD4high cells were also present (< or = 1% of CD4+ T cells) in vivo in BALB/c (H-2d) recipients of C57BL/6 (H-2b) skin allografts. CD4high T cells isolated from regional draining lymph nodes in these skin graft recipients reacted in a donor-specific fashion to C57BL/6 splenocyte stimulator cells in mixed lymphocyte culture. Adoptive transfer of CD4high, but not CD4normal T cells, just before skin engraftment in CD4 knockout mice, reconstituted rejection. The discovery that a small subpopulation of CD4high lymph node cells contained all of the alloantigen-specific T cells may allow study of tissue-specificity and subsequent alloantigen identification in transplantation.     

Evidence of T cell clonality in the infectious tolerance pathway: implications toward identification of regulatory T cells.

We have shown that a rare population of regulatory CD4+ T cells plays a key role in the acquisition of infectious tolerance in rat sensitized recipients of cardiac allografts pretreated with nondepleting anti-CD4 mAb. This study was designed to analyze the TCR Vbeta expression patterns in this transplantation model. First, we used Vbeta-specific RT-PCR to show that there was no differential usage of TCR Vbeta genes by T cells mediating rejection or tolerance. Indeed, graft-infiltrating lymphocytes expressed most of the 22 known rat TCR Vbeta genes in both recipient groups, suggesting unrestricted TCR Vbeta repertoire in alloreactive T cells. Then, we applied CDR3 spectrotyping of TCR beta-chain to assess the clonality of T cells at different anatomic sites. CDR3 size restriction, indicative of the presence of T cell clones, was observed in graft-infiltrating lymphocytes but not in draining lymph nodes or spleen of tolerant hosts. Consisent with the clonal expansion, T cells in tolerated grafts exhibited the memory phenotype at a much higher percentage as compared with peripheral lymphoid organs. Moreover, in tolerated graft-infiltrating lymphocytes, the CD3 size restriction occurred in limited Vbeta gene families, with Vbeta8.1 and Vbeta18 most frequently detected. Hence, T cells at the graft site of tolerant recipients contain T cell clones expressing selective Vbeta genes. This phenotypic characteristics of the tolerogenic GILs may potentially be used as a novel marker to identify operational regulatory T cells in organ allograft recipients.