The regulation of natural killer cell activity by splenic nonspecific suppressor cells and its modification in cancer patients

Spleen cells (SC), splenic venous blood lymphocytes (SVL) and peripheral blood lymphocytes (PBL) from gastric and esophageal cancer patients were simultaneously tested for natural killer (NK) and nonspecific suppressor (Ts) cell activities. Furthermore, the influence of Ts activity on the augmentation of NK activity by a biological response modifier (BRM) was also investigated. Positive Ts activities were frequently detected in the SC, SVL and PBL of advanced cancer patients. The NK activities of SC and SVL were maintained even in advanced cancer patients, though significantly depressed NK activities were observed in the PBL of advanced cases. Cancer patient SC, SVL and PBL with positive Ts activity showed low NK activities. Moreover, the NK activities of SVL and PBL were low in the patients with positive Ts activity in SC. The NK activity of normal control PBL was strongly augmented by interleukin 2, interferon and OK-432. These BRMs exhibited comparable capacities to augment the NK activities of SC, SVL and PBL with negative Ts activity in cancer patients, however, the effects of these agents seemed to be low in cells with a positive Ts activity. These results suggested that NK activity might be regulated by nonspecific suppressor cells and the presence of suppressor cells might affect the augmentation of NK activity through BRM in circulating blood lymphocytes and also in spleen cells.     

The activity of immunologic cells from peripheral blood, splenic venous blood and spleen in patients with advanced gastric cancer. A comparative study]

To elucidate the immunologic function of the spleen in AGC patients, peripheral blood lymphocytes (PBL), splenic venous blood lymphocytes (SVL) and spleen cells (SC) from 40 patients were tested for NK cell activity and T-cell subsets. Significant impairment of NK cell activity, decreased rate of CD+3 and CD+4 cells, declined CD+4/CD+8 ratio, and increased CD+8 cells were noted in SC of AGC patients as compared with PBL of normal subjects. NK cell activity and CD+4 cells of SVL and SC were significantly lower than those of PBL in AGC patients. More significant decline of CD+4/CD+8 cell ratio was found in SVL and SC when compared with PBL in AGC, mainly as a result of the marked decrease of CD+4 cells in SC. In conclusion, AGC tends to weaken the immune status of patients and the immunosuppressive role of the spleen would become more evident with the development of the tumor.     

Analysis of suppressor cell activities in spleen cells from gastric cancer patients and the effect of splenectomy on prognosis of gastric cancer

In gastric cancer patients, activities of Concanavalin-A induced suppressor cells ( ConAS ) and spontaneous suppressor cells (SpS) in spleen cells (SC), peripheral blood lymphocytes (PBL) and splenic vein lymphocytes (SVL) were comparatively investigated. Suppressions by ConAS in PBL were significantly increased in patients of Stages III and IV, while suppressions by SpS were increased in patients with recurrent tumors. Elevated activities of ConAS and SpS were observed in SCs and SVLs , respectively. ConAS activities were mostly indicated in the medium sized lymphocyte fractions which were fractionated on the basis of cell size, while SpS activities in the larger sized fraction. Cell numbers in the large sized lymphocyte fraction which contained higher proportion of Tg cells and OKT8 reactive T cells, tended to increase with advances of the disease. These results suggest that spleen contained much higher proportion of suppressor precursors which might be activated to become suppressor cells with advances of the disease. Furthermore, the effect of splenectomy on the prognosis of gastric cancer was investigated in randomized controlled trial. The patients who underwent total gastrectomy and had main location of the tumor on lesser curvature region were divided into two groups at random; splenectomy (+) and splenectomy (-) groups. A suggestive prolongation of survival time was observed in splenectomy (+) group. Thus, spleen seems to contribute to the immunosuppression in gastric cancer patients and splenectomy may lead to better prognosis.     

Antitumor Killer Lymphocytes in the Peripheral Blood of a Patient with Transitional Cell Carcinoma of the Bladder

Background: Peripheral blood lymphocytes (PBL) from patients with bladder cancer also contain cells possessing cytotoxic activity against autologous tumor cells. These cells are phenotypically heterogenous and include natural killer (NK) and cytotoxic T cells. This study investigated the role of cytotoxic lymphocytes directed against autologous bladder cancer cells.
Methods: PBL were obtained at intervals before and after surgery and analyzed for cytotoxic activity against autologous bladder cancer cells in 4-hour⁵¹ Cr release assay. PBL stimulated with autologous tumor cells were also transformed with human T-lymphotropic virus type-1, establishing a cell line (KB31) which was analyzed for phenotype and cytotoxic activity against the autologous tumor cells.
Results: PBL preoperative cytotoxic activity was low, but increased after surgery. Cytotoxic activity was found not only against autologous bladder cancer cells, but also against heterologous bladder cancer (KK-47) and myeloid leukemia (K562) cells, with the highest activity against the heterologous cell lines. The cytotoxic activity of KB31 was 40|X% against autologous tumor cells 6 weeks after initiation of the cell line, but decreased to 5|X% by 6 months. This activity was lower than that against the other cell lines, and was similar to that of PBL in short-term culture. Fluorescence-activated cell sorter (FACS) analysis demonstrated that in KB31 cells at 6 weeks, CD8+ cells were dominant, but CD56+ cells predominated at 6 months.
Conclusion: These results suggest that the presence of cytotoxic activity in the peripheral blood of the patient was due to both cytotoxic T cells and NK cells. The cytotoxic activity was lowest prior to surgery and increased postoperatively.     

Effects of serum immunosuppressive factors on the cytotoxicity of lymphokine-activated killer (LAK) cells induced by recombinant interleukin 2(R-IL2)

Fundamental studies were performed on adoptive immunotherapy, especially on effects on lymphocytic cytotoxic activity, of nonspecific immunosuppressive factors (ferritin, IAP, AFP) and of serum factors obtained from gastric cancer patients, and possible intervention of suppressor T cells in serum immunosuppressive activity on the cytotoxicity was also examined. The following results were obtained. 1) Cytotoxicity of LAK cells induced by culturing normal peripheral blood lymphocytes (PBL) with R-IL2 in the medium containing normal AB-type sera, was higher than that of PBL. 2) Effect of nonspecific immunosuppressive factors on cytotoxicity of LAK cells was lower than that on cytotoxicity of PBL. 3) Cytotoxicity of PBL was inhibited in a relatively specific fashion by sera from patients of the cancers which were of identical histological types with the target tumor cells, while that of LAK cells was hardly inhibited by patients' sera. 4) Cytotoxicity of Leu 15-PBL was inhibited by nonspecific immunosuppressive factors and also by cancer patients' sera in a relatively specific fashion in relation to histology. 5) Cytotoxicity of Leu 15-LAK cells was hardly inhibited by serum nonspecific and specific immunosuppressive factors. The above results showed that serum immunosuppressive factors might act on PBL cytotoxicity without intervention of suppressor T cells, and that LAK cells were hardly inhibited by such immunosuppressive factors. All these results suggested usefulness of adoptive immunotherapy with LAK.     

Activation by the protein-bound polysaccharide PSK (krestin) of cytotoxic lymphocytes that act on fresh autologous tumor cells and T24 human urinary bladder transitional carcinoma cell line in patients with urinary bladder cancer

PSK, a protein-bound polysaccharide Kureha, was tested for its ability to modulate the cytotoxicity of lymphocytes that act on autologous tumor cells and T24 human urinary bladder tumor cells in urinary bladder cancer patients in a 6-h 51Cr release assay. In vitro treatment of peripheral blood lymphocytes (PBL) with PSK for 18 hours resulted in an augmentation or induction of cytotoxicity against relatively resistant T24 cells in previously reactive and nonreactive cases, respectively. The PSK-treated PBL were able to kill more effectively tumor cells that were freshly isolated from the same cancer patients than non-treated PBL. The effects of PSK were noted with PBL as well as tumor infiltrating lymphocytes (TIL) and with PSK at concentrations of 10 to 100 micrograms./ml., while PSK at higher doses reduced their lytic activities. The addition of PSK to the assay at the same concentrations also enhanced the cytotoxicities. Autologous tumor killing (ATK) activities of both large granular lymphocytes (LGL) and T lymphocytes were enhanced by PSK. Treatment of PBL with PSK did not effect on the proportion of PBL binding to the tumor cells, while it augmented the cytotoxic activity. Cell-free supernatant of PSK-stimulated lymphocyte culture did not contain any detectable amounts of interferon-alpha (IFN-alpha), interferon-gamma (IFN-gamma) and interleukin-2 (IL-2). In addition, anti-IFN-alpha monoclonal antibody (MAb), anti-IFN-gamma MAb and anti-IL-2 MAb did not inhibit PSK-induced augmentation of cytotoxicity against T24. Oral administration of PSK (three gm./day) to patients with urinary bladder cancer daily for seven days before operation resulted in an augmentation of the cytotoxicity against T24 cells in five out of 10 patients and no change of the cytotoxicity in the other five patients. ATK activity was also enhanced by oral administration of PSK in three out of five patients. These results indicate that the antitumor activity of PSK may be in part mediated through activation of tumor killing system independent of IFN-alpha, IFN-gamma and IL-2.     

Role of natural killer cells in bladder tumor

The role of natural killer (NK) cells in bladder tumors was assessed from the aspect of local and systemic immune responses. The NK cell activity was measured in a 4-hour 51Cr-release assay. The NK activity in patients with bladder tumor was lower, though not significantly, than that in normal individuals. In patients with bladder tumor, the NK activity was significantly lower in invasive tumors and lymph node metastases. Moreover, the NK activity was lower in those who died (n = 4) than it was in survivors (n = 21). In an in vitro experiment, OK432 significantly augmented the NK activity in peripheral blood lymphocytes (PBL), however, this augmentation was not always OK432 dose-dependent. The augmented NK activity induced by OK432 occurred even in patients with invasive tumors. On the other hand, the spontaneous NK activity in tissue-infiltrating lymphocytes (TIL) and lymph node lymphocytes (LNL) was significantly lower than that in PBL. In these three groups, the NK activity was significantly increased by OK432, this rate of increase was highest in TIL, followed by LNL and PBL. Further studies are required to elucidate the role of NK cells in bladder tumor, from the aspect of local and systemic immune responses.     

Role of the spleen on immunosuppression in esophageal and gastric cancer

To elucidate the role of the spleen on immunosuppression of gastric and esophageal cancer, suppressor cell activities of spleen cells (SCs), splenic vein lymphocytes (SVLs) and peripheral blood lymphocytes (PBLs) were investigated. Concanavalin-A induced susppressor cell (Con-AS) activity of SCs was significantly higher in patients with gastric cancer than in those with benign diseases. Higher Con-AS activity of SCs was observed in esophageal cancer patients with tumors located in the lower portion of the esophagus. In comparison with suppressor activities of SCs and SVLs, the decrease of the predominance of suppressor precursors in SCs and the increase of the spontaneously activated suppressor cells in SVLs were noted with the advance of the tumors. Culture supernatants from splenic adherent cells significantly induced suppressor cell activities as well as did sera from splenic venous blood. From these results, it is concluded that the generation of suppressor precursors in the spleen is dependent on the location of tumors and that the maturation of suppressor cells occurs in the spleen by factors released from splenic adherent cells, then migrates into the peripheral blood.     

Natural killer activity of peripheral blood lymphocytes and its relation to histopathological factors of lung cancer

This investigation was intended to determine whether the natural killer (NK) activity of peripheral blood lymphocytes (PBL) correlated with the histopathological factor, which is thought to be a result of a balance between tumor aggression and host resistance. The NK activity of PBL from 60 patients with lung cancer was measured by the lysis of⁵¹Cr-labelled K562 target cells. The activity was significantly decreased with advancing stages of the disease, and inversely correlated with increased immunosuppressive substance levels of the serum. Histopathological factors, such as low grade pleural invasion of the tumor and abundant lymphoid cell infiltration around the tumor, were significantly associated with the high NK activity of PBL. These results show that a decrease in NK activity may play a role in identifying those individuals with a greater risk of cancer development.     

Analysis of suppressor T cells induced by donor-specific transfusion (DST): establishment of a human T cell hybridoma producing an antigen-nonspecific suppressor factor

Formation of suppressor T cells (Ts) induced by donor-specific transfusion (DST) is one of the most commonly suggested mechanisms for the beneficial effect of DST. In this study, we established a human T cell hybridoma derived from the peripheral blood lymphocytes (PBL) of a DST-treated patient, which produced an antigen-nonspecific suppressor factor. Post-DST PBL were fused with an azaguanine-resistant mutant of a human T cell leukemia cell line, CCRF-CEM^AG. After selection and cloning, we established one clone producing the mixed lymphocyte reaction (MLR) inhibitory factor (C524: 18%–43 % suppression). Suppressive activity of the supernatant obtained from C524 after activation by PHA was highly augmented (64%–88 % MLR suppression). This factor inhibited MLR dose-dependently in an antigen-nonspecific and HLA non-restricted manner. These results indicated that Ts clones could be generated in patients receiving DST and that the immunoregulatory factors produced by activated clones may play a role in the prolongation of renal allograft survival.     

Immunology of tumor infiltrating lymphocytes.

Frequently peripheral blood lymphocytes (PBL) do not reflect the tumor host relationship and cell mediated immunity in the PBL does not often correlate with prognosis. The tumor infiltrating lymphocytes (TIL) interact most closely with the tumor cells and are likely to more accurately reflect tumor host interactions. These studies indicate that TIL from pulmonary tumors are similar to PBL so far as their cell surface markers are concerned. The percentage of T-cells, B-cells, helper cells, suppressor cells, and NK cells are similar in the two compartments. However, the TIL are markedly suppressed in their functional capacity as measured by their proliferative and cytotoxic activity. In addition, natural killer (NK) cell activity is markedly diminished in TIL as opposed to the PBL. In addition, the direct injection of BCG into these tumors reverses this phenomenon by significantly increasing T-cell and NK cell functional activity. Thus, the microenvironment of the tumor profoundly affects the immunologic relationship between the tumor and the host.     

Induction of potent antitumour natural-killer cells from peripheral blood of patients with advanced prostate cancer

OBJECTIVE: To examine whether antitumour natural-killer (NK) cells can be induced from peripheral blood mononuclear cells (PBMCs) of patients with advanced prostate cancer, as cell therapy using antitumour immune cells is a promising candidate treatment but such patients generally have a suppressed immune response against cancer cells. PATIENTS AND METHODS: PBMCs were obtained from 10 patients (four with stage D2 and six with stage B or C disease). For the NK cell expansion, PBMCs were co-cultured with irradiated HFWT cells, a cell line originating from Wilms' tumour, in RHAM alpha culture medium supplemented with 5% autologous plasma and interleukin-2 (200 U/mL) for 2 weeks. RESULTS: When PBMCs were co-cultured with HFWT cells, lymphocytes from all patients had a 20- to 130-fold expansion after 2 weeks of culture. The CD16+ CD56+ cells constituted >70% of the proliferated lymphocyte population. The induced NK cells had significantly greater cytotoxicity against a prostate cancer cell line (PC-3) than lymphocytes cultured with no HFWT cells. There was no significant difference in growth and phenotypes of lymphocytes and the induced NK cell activity between patients with stage D2, B or C. CONCLUSION: NK cells with potent cytotoxic activity against prostate cancer cell lines from patients with advanced prostate cancer were selectively expanded. Further investigation is needed to determine whether this approach could be a candidate for cell therapy for advanced prostate cancer.     

Natural killer activity of peripheral blood lymphocytes and its relation to histopathological factors of lung cancer

This investigation was intended to determine whether the natural killer (NK) activity of peripheral blood lymphocytes (PBL) correlated with the histopathological factor, which is thought to be a result of a balance between tumor aggression and host resistance. The NK activity of PBL from 60 patients with lung cancer was measured by the lysis of 51Cr-labelled K562 target cells. The activity was significantly decreased with advancing stages of the disease, and inversely correlated with increased immunosuppressive substance levels of the serum. Histopathological factors, such as low grade pleural invasion of the tumor and abundant lymphoid cell infiltration around the tumor, were significantly associated with the high NK activity of PBL. These results show that a decrease in NK activity may play a role in identifying those individuals with a greater risk of cancer development.     

Preventive effect of a traditional herbal medicine,Hochu-ekki-to,on immunosuppression induced by surgical stress

Purpose To examine the effect of preoperative administering of a Japanese traditional herbal medicine, Hochu-ekki-to (TJ-41), on immunosuppression induced by surgical stress in patients with gastrointestinal malignancies. Methods To monitor the immune functions, the mitochondrial membrane potential (MMP) and natural killer (NK) cell activity prior to and following operation were measured in peripheral blood lymphocytes (PBL) in patients with (n = 20) or without (n = 27) the preoperative administering of TJ-41 for 7 days. The plasma catecholamine and interleukin (IL)-6 levels were also analyzed prior to and following the operation. Results The numbers of MMP-high CD56-positive cells (NK cells) and NK cell activities in the TJ-41-treated group were significantly higher than those in the control group (P = 0.026 and P = 0.037, respectively). An elevation of plasma noradrenaline and IL-6 following surgery was also inhibited by the preoperative administering of TJ-41 (P = 0.023 and P = 0.039, respectively). A positive correlation between MMP-high CD56-positive cell numbers and NK cell activity in PBL treated with carbonyl cyanide m-chlorophenyl hydrazone (CCCP) in vitro suggested that MMP measurement in CD56-positive cells can serve as a convenient alternative to evaluate the NK cell activity. Conclusion Our findings suggest that the preoperative administering of TJ-41 prevents surgical stress-induced immunosuppression by maintaining the NK cell activity and inhibiting the elevation of stress mediators.     

Role of the spleen on immunosuppression in esophageal and gastric cancer

To elucidate the role of the spleen on immunosuppression of gastric and esophageal cancer, suppressor cell activities of spleen cells (SCs), splenic vein lymphocytes (SVLs) and peripheral blood lymphocytes (PBLs) were investigated. Concanavalin-A induced suppressor cell (Con-AS) activity of SCs was significantly higher in patients with gastric cancer than in those with benign diseases. Higher Con-AS activity of SCs was observed in esophageal cancer patients with tumors located in the lower portion of the esophagus. In comparison with suppressor activities of SCs and SVLs, the decrease of the predominance of suppressor precursors in SCs and the increase of the spontaneously activated suppressor cells in SVLs were noted with the advance of the tumors. Culture supernatants from splenic adherent cells significantly induced suppressor cell activities as well as did sera from splenic venous blood. From these results, it is concluded that the generation of suppressor precursors in the spleen is dependent on the location of tumors and that the maturation of suppressor cells occurs in the spleen by factors released from splenic adherent cells, then migrates into the peripheral blood.     

The immunologic profile of anesthetists

Reports in the literature have suggested possible impairment of immunocompetence in operating theater personnel. In a group of 18 physician anesthesiologists the following were determined: hemoglobin concentration; white blood cell count; numbers of T, B, and natural killer (NK) lymphocytes; number of T-active cells; and numbers of T-helper/inducer (Th) and T-suppressor/cytotoxic (Ts) cells; and the Th/Ts ratio. Function of T lymphocytes was evaluated using the local xenogeneic graft-versus-host reaction and spontaneous suppressor or helper activity of T cells. The same parameters were determined in a group of 18 age- and sex-matched healthy controls. It was found that no matter what their age or how long they have been engaged in anesthetic practice, anesthetists show no immunosuppression as evidenced by these parameters.     

A clinical study of immunological status in patients with gastric cancer: with special reference to T-cell subsets, interleukin-2 in the lymphocytes of peripheral blood

Peripheral blood lymphocytes of 63 patients with gastric cancer were studied by using different monoclonal antibodies and flow cytometry. Used monoclonal antibodies were OKT3 (total T cell), OKT4 (helper/inducer), OKT8 (suppressor/cytotoxic), Leu 7 and Leu 11 (NK/K cell). Interleukin-2 was measured by tritium-labelled thymidine CTLL assay on the supernatant of peripheral blood lymphocytes after 24 hours stimulation with phytohemagglutinin. Interleukin-2 receptor was also studied by using monoclonal antibody (for Tac antigen) and flow cytometry. The results were as follows: among peripheral blood lymphocytes; 1. the number of OKT3, OKT4 cells and the percentage of OKT4 cells decreased significantly with more advanced stage of cancer. 2. production of interleukin-2 also decreased with the progression of the cancer. 3. decreases in the OKT4/OKT8 ratio were found with cancer progression. 4. the percentage and the number of OKT8 cells increased. 5. the percentage and the number of Leu 11 cells and the number of Leu 7 cells were increased significantly in the stage III (moderately advanced cancer). These results suggested that the activated helper T cells decreased, the induction capability of cytotoxic T cells decreased and the suppressor T cells increased with the progression of cancer. Quantitative and qualitative change in T-cell subsets in advanced stage may be one factor responsible for immunosuppression.     

Immunological significance of splenectomy in gastric cancer surgery. Production of immunosuppressive factor in the spleen

We studied immunological significance of splenectomy in gastric cancer surgery with special reference to serum suppressor factor. The results showed that the sera from splenic venous blood in advanced gastric cancer was more suppressive to PHA blastogenesis of normal lymphocytes and also higher in the values of circulating immune complexes, as compared to the sera from peripheral blood. Furthermore, the media from cultures of spleen cells of patients with advanced gastric cancer indicated to suppress PHA blastogenesis of normal lymphocytes, as compared to the media from cultures of peripheral lymphocytes of the same patients. The suppressive activity was more increased in the media from cultures of nonadherent cell population obtained from the spleen cells. From these data, it was suggested that the spleen of patients with advanced gastric cancer was capable of producing serum suppressor factor. Therefore, gastrectomy combined with splenectomy may be reasonable in patients with advanced gastric cancer.     

The role of lymphocyte surface binding sites for wheat germ agglutinin in the negative regulation of cancer patients

The role of lymphocyte surface binding sites for wheat germ agglutinin (WGA) in the negative regulation of cancer patients was investigated. The number of WGA binding sites on the surface of each lymphocyte ranged from 10⁷ to 10⁸. Fluorescein isothiocyanate (FITC)-conjugated WGA, bound to the majority of peripheral blood lymphocytes (PBL) with two peaks of fluorescent intensity was expressed either dimly or brightly. The increase in lymphocytes brightly expressing WGA fluorescent intensity (WGA bright lymphocytes) significantly correlated with the number of WGA binding sites. The suppression of lymphocyte proliferation mediated by the purified soluble suppressor factor (SSF) significantly correlated with an increase in the WGA bright lymphocyte population (P<0.05). A significantly greater number of WGA bright lymphocytes in PBL was found in patients with esophageal, gastric, breast, or colon cancer, than in those with benign diseases or in healthy controls. Furthermore, an increase in WGA bright lymphocytes was found in subsets expressing the antigens CD8 dimly or CD16. Thus, it is suggested that the number of WGA binding sites may increase mainly on the surface of effector cells such as NK cells and CD8-positive killer T cells in cancer patients, triggering the negative regulation mediated by SSF.     

Decreased circulating large granular lymphocytes associated with depressed natural killer cell activity in renal transplant recipients

Renal transplant recipients (RTR) receiving prednisone and azathioprine (AZ) frequently have depressed natural killer (NK) cell activity. In humans, NK activity is mediated by the large granular lymphocyte (LGL). To determine the mechanism of depressed NK activity among RTR, we quantitated the NK activity of peripheral blood lymphocytes (PBL) and the percentage of circulating LGL in Giemsa-stained cytocentrifuge preparations of PBL from 20 RTR and 6 healthy volunteers. In addition, the PBL were incubated with 1000 U/ml IFN beta to assess augmentation of NK activity. Finally, single-cell cytotoxicity assays in agarose using highly purified LGL from our study subjects were performed to assess the ability of the LGL to bind and to kill the K562 target cells. Mean (+/- 1SD) NK activity at a 50:1 effector-to-target ratio using K562 targets was 51.2 +/- 21.8% among normals and 12.9 +/- 10.3% in RTR, and it was augmented to 60.5 +/- 13.1% and 17.5 +/- 10.3%, respectively, following interferon (IFN) exposure. Mean percentage of LGL among PBL in normals was 13.2 +/- 1.2%, and 4.0 +/- 1.7% in RTR. A significant correlation existed (R = 0.90) between NK activity and the numbers of LGL (P less than .001). In two patients, NK activity following cessation of azathioprine and prednisone increased significantly (P less than .005), and an increase of LGL from 6%-30% among PBL accompanied the increase in NK activity in one patient. Incubation with IFN boosted this patient's NK activity from 22% to 62%, suggesting the presence of circulating pre-NK cells among the LGL. There was no significant difference in the binding or killing of K562 targets by LGL in single-cell assays comparing RTR with normal controls (P greater than 0.1), indicating normal functioning LGL in our study subjects. These results indicate that decreased circulating LGL among RTR receiving AZ and prednisone is associated with depressed NK activity. The ability of IFN to augment the NK activity of RTR significantly suggests the presence of circulating pre-NK cells. Finally, the rebound of both the circulating number of LGL and the NK activity after cessation of immunosuppressive drugs suggests a direct effect of those drugs in the inhibition of NK in RTR.