Cell-mediated immune reaction against tumors induced by oncornaviruses. II. Nature of the effector cells in tumor-cell cytolysis

The nature of the effector cells detected by the chromium release test (CRT) has been studied in BALB/c and C57Bl/6 mice bearing murine sarcoma virus (MSV)-induced tumors. Anti-θ-C3H immune sera completely inhibited the cytotoxic activity of lymphoid cells in the presence of complement; anti-immunoglobulin sera failed to decrease this activity. No activation of normal non-sensitized lymphoid cells in the presence of heat-decomplemented sera from mice bearing MSV-induced sarcomas could be obtained. Identical results have been found in allogeneic systems with major H-2 histocompatibility antigens. It can be concluded that a thymus-processed lymphoid cell sub-population sharing the θ antigen is exclusively or very predominantly responsible for the immune cytolysis both in syngeneic tumor systems and in allogeneic transplantation systems.     

Loss of marrow allograft resistance in mice with transplanted methylcholanthrene-induced sarcomas.

To determine if the effector cells responsible for allogeneic marrow stem cell rejections were suppressed in mice with tumors, C57BL/6 (B6) mice were inoculated with 3-methylcholanthrene (MCA)-induced sarcoma cells. When the tumor reached 2.0--2.5 cm in diameter, these mice and control B6 and (BALB/c times A)F1 (CAF1) uninoculated animals were irradiated and given BALB/c marrow cells in the first of a two-step "stem cell rescue" experiment. Four days later, spleen cells of the primary hosts were reinoculated into irradiated CAF1 secondary hosts compatible with BALB/c marrow cells and immunized against B6 antigens. Splenic uptake (percent) of 125I-5-iodo-2'-deoxyuridine 5 days after spleen cell regrafting was used as a measure of cell proliferation and reflected growth of the stem cells in the primary hosts. BALB/c stem cells grew as well in B6 mice with tumors as in CAF1 primary hosts but were rejected by B6 controls. Seeding efficiency of BALB/c stem cells 6 hours after infusion of marrow cells and growth of syngeneic B6 stem cells were enhanced twofold in spleens of tumor-bearing B6 mice. To exclude the possibility that enhanced seeding resulted in greater survival of allogeneic stem cells, more DBA/2 marrow cells were infused into control B6 primary hosts than into tumor-bearing B6 and control DBA/2 mice. Control B6 mice resisted growth of even 7.5 times 10(6) DBA/2 marrow cells, whereas B6 tumor bearers allowed growth of 2.5 times 10(6) cells. No "suppressor cells" capable of inhibiting marrow cell allograft reactions were detected in spleens of tumor-bearing mice. Thus transplanted syngeneic MCA-induced sarcomas abrogated the ability of mice to reject allogeneic marrow stem cells.     

Cell-mediated cytotoxicity to moloney sarcoma in syngeneic and allogeneic rats

Cell-mediated cytotoxicity in the primary immune response to Moloney sarcoma tumor (MST) in allogeneic and syngeneic rats was found to be predominantly T-cell-dependent. A minor non-T-cell cytotoxic activity may also have been detected. CMC was presumably directed against tumor and viral related antigens in the syngeneic host and primarily against alloantigens in the allogeneic host. CMC was more vigorous in the allogeneic recipient than in the syngeneic host. This may be due to differences in quantities or immunogenicities of the various antigens involved. Two peaks of T-cells in effector populations were observed during a 20-day post-inoculation period. The first peak corresponded to peak T-cell-mediated cytotoxicity on day 8 and the second peak occurred on days 13 or 14 when CMC was minimal or undetectable.     

Detection of a unique antigen on radiation leukemia virus-induced leukemia B6RV2

Radiation leukemia virus-induced leukemia of a male C57BL/6 mouse, B6RV2, is immunogenic to female BALB/c X C57BL/6 F1 mice. In these mice, B6RV2 tumors regressed after initial growth, and after tumor regression the mice were resistant to repeated inocula of up to 10(8) B6RV2 cells. Serum from these mice reacted with B6RV2 in mixed hemadsorption or protein A assays, and absorption analysis indicated that the antigen was restricted to B6RV2; it could not be detected in normal thymocytes or spleen concanavalin A blasts from different inbred strains, nor in 16 C57BL/6 or BALB/c leukemias. Spleen cells from mice in which the tumor had regressed were cytotoxic to B6RV2 after in vitro stimulation with B6RV2, as shown by 51-chromium release assay. This cytotoxicity was eliminated by pretreatment of the cells with anti-Thy-1.2, anti-Lyt-2.2, anti-Lyt-3.2, and complement, indicating that the effector cells were T-cells. The specificity of T-cell killing of B6RV2 was examined by competitive inhibition assays with unlabeled cells; only B6RV2 inhibited killing, while eight other C57BL/6 leukemias did not inhibit. Thus, the antigen on B6RV2 defined serologically and by cytotoxic T-cells is a unique antigen. However, it was not revealed by antibody-blocking test whether the unique determinant defined serologically was related to that recognized by T-cells; B6RV2 antiserum did not block lytic activity in the absence of added complement, irrespective of whether the target cells were untreated or anti-H-2b-treated B6RV2. H-2Kb antisera, but not H-2Db antisera, blocked lysis. This indicated that the H-2Kb molecule was exclusively involved in recognition of B6RV2 by cytotoxic T-cell.     

Antigenic changes of DBA/2J mastocytoma cells when grown in the BALB/c mouse.

A 10-day growth period of the DBA/2J strain-specific P815-X2 mastocytoma in the BALB/c mouse altered the antigenicity of the tumor cell surface. The in vivo-modified mastocytoma cells differed from mastocytoma cells grown in the original DBA/2J mice in suspectibility to lysis by immune peritoneal exudate cells, in vitro antigenic recognition by cytotoxic T-cells, and immunizing capacity in allogeneic C57BL/6 mice. Propagation of the altered tumor cells in the original host or maintenance in tissue culture for 40 hours restored complete susceptibility to lymphocyte-mediated cytotoxicity.     

Alloreactivity and tumor antigens: generation of syngeneic antilymphoma killer lymphocytes by alloimmunization of mice with normal cells

The possibility of obtaining a syngeneic antitumor effect by immunization with normal allogeneic cells was investigated by tests of the lytic activity of peritoneal exudate cells (PEC) of BALB/c mice immunized with lymphoid cells of either a single strain or a pool of six different allogeneic strains on the syngeneic Moloney virus-induced lymphoma YC8 target and on one of its clones designated YC8-D1. Significant cytotoxicity on both targets but not on two other BALB/c lymphomas was obtained with PEC of BALB/c mice singly immunized to the non-H-2-incompatible but H-2-compatible DBA/2 or B10.D2 lymphoid cells. The lack of lysis of YC8 cells by PEC of BALB/c mice immune to B10.A (H-2k,d) suggests that the in vitro killing was restricted by Kd-IEd region products of the major histocompatibility complex. Pool immunization was effective in generating antitumor cytotoxic lymphocytes only when DBA/2 lymphoid cells were included in the pool. The pattern of reactivity of effectors elicited in (BALB/c x DBA/2)F1 and in (BALB/c x B10.D2)F1 mice by immunization with DBA/2 and B10.D2 cells showed that at least two sets of antigens are recognized on YC8 targets, one shared by DBA/2 and B10.D2 tissues and the other expressed by DBA/2 cells only. Cold target blocking experiments indicated that the same effectors recognized non-H-2 antigens of DBA/2 and the cross-reacting YC8 determinants. The antitumor effect was mediated by T-cells, since it was abrogated by treatment of effectors with anti-Thy 1.2 serum plus complement. These data indicate that determinants defined by cytotoxic T-lymphocytes are expressed on the BALB/c lymphoma YC8 and cross-react with non-H-2 antigens of DBA/2 and B10.D2 strains.     

Characterization of interleukin 2-dependent cytotoxic T-cell clones: specificity, cell surface phenotype, and susceptibility to blocking by Lyt antisera

Cytotoxic T-cells were derived from the peritoneal cavity of a C57BL/6 mouse immunized with BALB/c sarcoma Meth A and from the spleens of BALB/c x C57BL/6 F1 (hereafter called CB6F1) mice immunized with BALB/c leukemia RL male 1. The cells were cultured in interleukin 2 and cloned by limiting dilution, and their specificity was determined by direct tests and competitive inhibition assays. C57BL/6 anti-Meth A effector cells recognized H-2Dd determinants. CB6F1 anti-RL male 1 effector cells recognized a unique cell surface antigen of leukemia RL male 1. The specificity was maintained in long-term culture. The cell surface phenotype of the cloned effector cell lines as determined by absorption analysis was Thy-1.2+, Lyt-1.2+, 2.2+, and 3.2+. Cytotoxicity was blocked at the target cell level by antisera against H-2Dd, but not H-2Dk or H-2b, and at the effector cell level by antisera against Lyt-2.2 and 3.2, but not Lyt-1.2, Ly-5.1 or Thy-1.2.     

Effect of adult thymectomy on tumour immunity in mice.

The effect of adult thymectomy in DBA/2J mice on the in vitro response to syngeneic tumour cells was investigated. Spleen cells from adult mice which had been thymectomized 8 weeks previously demonstrated a severely impaired primary cytotoxic response to P815 tumour cells, whereas their cytotoxic responses to allogeneic cells (C57BL/6) and to non-H-2 antigens (BALB/c), and their ability to form a primary antibody response to sheep red blood cells was unimpaired. Suppressor T cells, specific for P815 cells, appeared early in the thymuses of animals inoculated with P815 cells (between 4 and 8 days after tumour-cell injection). No differences in tumour growth between animals thymectomized as adults and sham-operated controls were observed, and thymectomized tumour-bearing animals had levels of specific suppressor cells in their lymph nodes equivalent to the levels found in untreated controls. Severely thymocyte-deprived animals which had been thymectomized, irradiated and reconstituted with either marrow or spleen cells 8 weeks before tumour implantation succumbed more rapidly to metastatic tumour than did control animals.     

Effect of BCG on alloimmune cell-mediated cytotoxicity in (C57BL/6Jfemale x A/Jmale)F1 mice. II. Correlation with BCG activity in syngeneic tumor systems.

The effectiveness of selected BCG regimens to produce an activation of cell-mediated cytotoxicity (CMC) in an allogeneic tumor system was compared with its ability to cause tumor regression in syngeneic tumor systems. In the tumor system selected in both inbred LEW rats and inbred C57BL/6J and (C57BL/6Jfemale x A/Jmale)F1 mice, a correlation was observed in that BCG treatments that caused marked CMC activation in the allogeneic tumor systems also effectively caused tumor regression and increased animal survival in syngeneic systems. It was concluded that the allogeneic CMC reaction can be used to predict the capacity of BCG to cause tumor rejection.     

Embryonic antigens shared between chemically induced lymphosarcomas and fibrosarcomas of the mouse.

An antiserum obtained by the immunization of C57BL/HeDp mice with a pool of C3HF/Dp 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced fibrosarcomas exerted a specific cytotoxic activity in vitro on C57BL/HeDp chemically induced lymphosarcomas. Conversely, C57BL/HeDp spleen cells sensitized against C3Hf/Dp chemically induced lymphosarcomas or embryo cells were cytotoxic for plated cells of syngeneic DMBA-induced fibrosarcomas. Absorption studies with antiembryo and antilymphoma antisera showed that embryonic antigens were shared between lymphosarcomas and fibrosarcomas and that all serologically defined antigens present on lymphoma cells, including virus-related antigens, were also on fibrosarcoma cells.     

Effect of immunotherapy with allogeneic lymphokine-activated killer cells and recombinant interleukin 2 on established pulmonary and hepatic metastases in mice

The adoptive transfer of lymphokine-activated killer (LAK) cells in conjunction with the systemic administration of recombinant interleukin 2 (RIL-2) results in the regression of established pulmonary and hepatic micrometastases from a variety of immunogenic and nonimmunogenic murine tumors in syngeneic C57BL/6 mice. Recent studies have shown that this therapeutic approach can mediate the regression of cancer in humans as well. Because of the practical difficulties in obtaining syngeneic or autologous LAK cells for the therapy of cancer in humans we have now evaluated the antitumor efficacy of allogeneic LAK cells generated from different strains of mice. The in vitro lysis of fresh tumor targets by LAK cells is not a major histocompatibility complex-restricted phenomenon since LAK cells of BALB/c-H-2d, DBA/2-H-2d, and C3H-H-2k origin all exhibited lytic activity when tested against allogeneic MCA-102-H-2b tumor cells in short term 51Cr release assays. In vivo, the i.v. transfer of allogeneic LAK cells combined with i.p. injections of RIL-2 reduced the number of established pulmonary metastases induced by either MCA-105 or MCA-101 tumors which are syngeneic to C57BL/6 hosts. The extent of reduction of these pulmonary metastases by the allogeneic LAK cells was directly dependent upon the dose of RIL-2 given; increasing doses of systemically administered RIL-2 resulted in increasingly greater reduction in the numbers of established 3-day pulmonary sarcoma metastases. In dose titration experiments, adoptive transfer of at least 2 doses of 10(8) allogeneic LAK cells was necessary to achieve significant antitumor effect in vivo. Allogeneic LAK cells were also successful in mediating significant regression of hepatic micrometastases. Again, the i.v. transfer of allogeneic LAK cells had a smaller therapeutic benefit compared to i.v. transfer of syngeneic LAK cells. When allogeneic LAK cells were injected intraportally, however, they were as effective as syngeneic LAK cells. Allogeneic LAK cells had little, if any, therapeutic effect on established pulmonary and hepatic metastases when administered to recipients previously immunized to the histocompatibility antigens on the donor cells. Taken together, our results indicate that allogeneic LAK cells from several strains of mice are effective in lysing fresh MCA-102 tumor in vitro and that when given i.v. in sufficient numbers, in conjunction with RIL-2, they can mediate significant reduction in the number of established pulmonary and hepatic micrometastases in nonalloimmunized C57BL/6 mice.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunization with interleukin-2-secreting allogeneic mouse fibroblasts expressing melanoma-associated antigens prolongs the survival of mice with melanoma

The survival of C57BL/6 mice (H-2^b) bearing B16 melanoma (H-2^b) was prolonged if the animals were treated solely by immunization with an interleukin-2 (IL-2)-secreting allogeneic cell construct that expressed melanoma-associated antigens (MAA) along with major histocompatibility complex (MHC) class-l determinants (H-2^k; RLBA-IL-2 cells). This was the case if the mice were immunized simultaneously with, or 6 days following, the injection of viable B16 cells. Under similar conditions, the survival of tumor-bearing mice immunized with an allogeneic cell construct (H-2^k) that expressed MAA but did not secrete IL-2 (RLBA-ZipNeo cells), or with an allogeneic construct (H-2^k) that secreted IL-2 but did not form MAA (LM-IL-2 cells), was also prolonged. However, in these instances, the period of survival was significantly shorter than that of mice immunized with the cell construct that combined IL-2 secretion with the expression of MAA. Tumor-bearing mice immunized with non-transfected LM(TK-) cells (H-2^k), or irradiated B16 cells (H-2^b) failed to survive longer than untreated mice. Although the survival of the treated animals was prolonged, in most instances tumor growth recurred. The recurrent tumors in mice treated with the allogeneic cell constructs formed melanin and were histologically indistinguishable from tumors in untreated mice. Cells from the recurrent tumors were resistant to further immunotherapy and to cytotoxic effector cells obtained from the spleens of mice immunized with the same cellular immunogen used initially. The injection of IL-2-secreting syngeneic B16 cells into C57BL/6 mice invariably resulted in the appearance of non-IL-2-secreting melanomas. Under similar circumstances, tumors failed to develop in C57BL/6 mice injected with IL-2-secreting, or non-secreting, allogeneic cell constructs. Thus, the expression of allogeneic antigens protected the mice from growth of the cellular immunogens.     

Augmentation of tumor immunity against syngeneic tumors in mice by beta-carotene

The effect of beta-carotene on tumor immunity was examined with the use of a syngeneic murine tumor system. Oral administration of beta-carotene (120 micrograms/mouse/day) for 9 days from day 1 to the BALB/c mice inoculated sc with 10(7) syngeneic BALB/c Meth A fibrosarcoma cells (Meth A) led to a remarkable rejection against rechallenged Meth A implanted sc on day 10. The growth of Meth 1 fibrosarcoma (Meth 1), another syngeneic tumor of BALB/c origin, as a rechallenge tumor was unaffected by treatment with beta-carotene, thereby suggesting that beta-carotene may augment tumor rejection specific to tumor-specific antigens. Winn assay revealed that the suppressive effect on tumor growth of immune lymph node cells obtained from Meth A-inoculated beta-carotene-treated mice on day 12 was enhanced dose dependently. Primary effector cells responsible for the augmented rejection are Thy-1-positive, Lyt-1-negative, and Lyt-2-positive lymphocytes, presumably cytotoxic T-lymphocytes.     

Immunity to B16 melanoma in mice immunized with IL-2-secreting allogeneic mouse fibroblasts expressing melanoma-associated antigens

Co-presentation of weak tumour-associated antigens along with strongly immunogenic determinants leads to the development of an anti-tumour immune response in recipients syngeneic with the tumour. Tumour immunity develops in mice immunized with tumour cells modified by the introduction of cDNA for interleukin-2 (IL-2). Here, we report the anti-tumour response following immunization with an IL-2-secreting cell construct that expresses tumour-associated antigens, along with allogeneic major histocompatibility antigens. The construct was prepared by transfecting LM(TK^?) mouse fibroblasts (H-2^k) with genomic DNA from B16 melanoma cells syngeneic in C57BL/6J mice (H-2^b). Transfectants expressing melanoma-associated antigens (MAA) were then infected with an expression-competent retroviral vector containing a cDNA specifying human IL-2. Cytotoxicity toward B16 cells was detected for as long as 5 months in both spleen and macrophage cell populations in C57BL/6J mice immunized with the IL-2-secreting, cells. Mice immunized with non-IL-2-secreting, MAA-positive allogeneic cells developed melanoma immunity as well, but to a lesser extent. Immunity to 2 tumour-cell lines expressing the H-2^d haplotype and to YAC-I cells was detected in peritoneal macrophages, but not in spleen cells from C57BL/6J mice immunized with the cell construct, indicating that the response to B16 cells was only partially specific. C57BL/6J mice immunized with the IL-2-secreting cell construct survived significantly longer, following an injection of viable B16 cells, than mice in various control groups. The contribution of allogeneic antigens to the melanoma immunity was indicated by the failure of mice syngeneic with LM(TK^?) cells to develop melanoma immunity following immunization with non-IL-2-secreting, MAA-positive cell constructs. The formation of IL-2 partially compensated for the lack of allogeneic antigens.     

Inhibition of established transplants of chemically induced sarcomas in syngeneic mice by lymphocytes from immunized donors

Intravenous injections of lymph node cells from immunized BALB/c and (C57BL/-6 X A) F₁ mice and from immunized sheep induced regression or inhibition of established grafts of a methylcholanthrene-induced sarcoma in syngeneic BALB/c mice.     

In vitro generation of primary and secondary cytotoxic cell-mediated immune responses to chemically induced mouse sarcomas

Mixtures of lymph node and spleen cells from normal (untreated) BALB/c mice and from BALB/c mice whose syngeneic tumors had been excised 7–28 days previously (“tumor-excised mice”), were sensitized in vitro by cultivation for 9 days with cells from syngeneic, methylcholanthrene-induced sarcomas. The in vitro- sensitized lymphoid cells were tested in a 36-h microcytotoxicity assay for reactivity against target cells carrying the sensitizing tumor antigens, as well as against control target cells lacking these antigens. After co-cultivation with tumor cells, lymphoid cells from both normal and tumor-excised mice were cytotoxic to tumor cells carrying the sensitizing antigens. The cytotoxicity was generally specific, and occurred at low effector: target cell ratios (in some experiments down to 1:1). When lymphoid cells from tumor-excised mice were exposed in vitro for 9 days to cells carrying the same antigens as those which were originally present on the surgically excised tumors, the effector cells obtained gave a dose-dependent cytotoxic response suggestive of a linear relationship. When lymphoid cells from normal mice were similarly sensitized for 9 days, specifically cytotoxic lymphoid cells were generated but no linear dose-dependent response was detected.     

Destruction of experimental malignant melanoma by mediators of cellular immunity.

Listeria monocytogenes (LM) in admixture with B-16 melanoma suppresses local tumor development in syngeneic C57BL/6 mice. In vitro, LM-immune peritoneal and splenic cells are cytotoxic to B-16. Induction of cell-mediated immunity to LM antigens are required for the killing effect, since effector cells from LM-"immune" athymic nude mice are unable to kill tumor cells in vitro. Further, elimination of macrophages by a specific antiserum plus complement abrogates the cytotoxic effect of peritoneal cells. Peritoneal or splenic adherent or nonadherent cells are not cytotoxic, whereas combination of these two cell populations in the presence of the specific antigen can kill the B-16 target cells. A factor, probably lymphotoxin, released by the intact effector cells in the culture fluid mediates tumor cell destruction in vitro. Production of this factor requires cooperation of macrophages with specifically sensitized thymus-derived cells.     

Activation in vitro of mouse macrophages by syngeneic, allogeneic, or xenogeneic lymphocyte supernatants.

Macrophages from normal C57BL/6 mice, those with a subcutaneous B16 melanoma, and mice immunized against the tumor were examined for in vitro cytotoxicity to B16 tumor cells. Macrophages were treated by incubation with supernatants from B16 cells grown either in unmixed cultures or in cultures containing syngeneic, normal, or sensitized allogeneic (A mouse), or xenogeneic (rat) lymphocytes. The various treated and untreated macrophages were then cultured for 5 days with viable B16 cells prelabeled with 125I-5-iodo-2'-deoxyuridine; the cultures were terminated, and the extent of destruction of the B16 target cells was determined from the amounts of radioactivity remaining in adherent tumor cells. Of the untreated macrophages, only those from immunized mice were cytotoxic to the tumor cells; macrophages from normal and tumor-bearing mice became cytotoxic by incubation with supernatants from cultures containing lymphocytes from immunized syngeneic mice, sensitized allogeneic mice, or sensitized rats; and macrophages incubated with supernatants from cultures containing normal nonsensitized allogeneic or xenogeneic lymphocytes showed no cytotoxicity. Thes results suggested that macrophages from tumor-bearing animals are potentially cytotoxic to their syngeneic tumors and can be activated by mediators released from sensitized syngeneic, allogeneic, and/or xenogeneic lymphocytes in vitro.     

Factors affecting suppressor cell activity in tumor-allosensitized mice

Adult C57BL/6 mice inoculated with P-815 mastocytoma cells developed splenic suppressor cells. These suppressor cells were assayed in mixed lymphocyte cultures. Suppressor cells appeared earlier and became more active after sensitization with low doses of allogeneic tumor. After low doses of tumor cells, the suppressor cell activity developed before cytotoxic activity, whereas after higher doses of tumor cells, suppressor and cytotoxic activity appeared simultaneously. The suppressor cells were not H-2 restricted but did express their activity stronger in the presence of the specific (H-2d) alloantigen. Neonatally thymectomized adult C57BL/6 mice failed to develop splenic suppressor cell activity after tumor allosensitization. This suggested that the thymus is a source for suppressor precursor cells. These precursor cells remained active in the spleen up to 3 1/2 months after adult thymectomy. Suppressor factor was released in cultures of tumor-allosensitized spleen cells. The presence of a specific (H-2d) alloantigen improved the relase of suppressor factor (SF). Cultures of tumor-allosensitized spleen cells, enriched for T-cells, contained more SF. SF was not H-2 restricted or antigen-specific.     

Genetic control of hapten-reactive helper T-cell responses and its implications for the generation of augmented antitumor cytotoxic responses

The genetic control of hapten-reactive helper T-cell activity involved in cytotoxic T-lymphocyte (CTL) responses and its implications for augmenting tumor-specific immunity were studied. C57BL/6N mice were immunized to trinitrophenyl (TNP) or N-iodoacetyl-N'-(5-sulfonic l-naphthyl)ethylenediamine (AED) hapten by inoculation of hapten-modified syngeneic spleen cells. Spleen cells from these hapten-immunized mice were tested for hapten-reactive helper T-cell activity for generation of CTL. TNP-primed spleen cells resulted in only marginal help for the generation of anti-TNP-modified syngeneic spleen cell (TNP-self) CTL response when cocultured with normal C57BL/6N spleen cells (responding cells) in the presence of TNP-self. In contrast, AED-primed spleen cells exhibited appreciable help for AED-induced CTL responses. Furthermore, AED-helper, but not TNP-helper, T-cell activity was demonstrated to augment the generation of antitumor (RBL-5 leukemia) CTL responses from normal syngeneic spleen cells when stimulated with the corresponding hapten-self plus RBL-5 tumor cells. These results indicate that the successful augmentation of syngeneic tumor immunity through T-T-cell interaction with the use of hapten-reactive helper T-cells can depend on selection of the appropriate haptenic reagent in an individual expressing a given major histocompatibility haplotype.