Clonal Expansions of CD8+ T Cells with IL-10 Secreting Capacity Occur during Chronic Mycobacterium tuberculosis Infection

The exact role of CD8⁺ T cells during Mycobacterium tuberculosis (Mtb) infection has been heavily debated, yet it is generally accepted that CD8⁺ T cells contribute to protection against Mtb. In this study, however, we show that the Mtb-susceptible CBA/J mouse strain accumulates large numbers of CD8⁺ T cells in the lung as infection progresses, and that these cells display a dysfunctional and immunosuppressive phenotype (PD-1⁺, Tim-3⁺, CD122⁺). CD8⁺ T cell expansions from the lungs of Mtb-infected CBA/J mice were also capable of secreting the immunosuppressive cytokine interleukin-10 (IL-10), although in vivo CD8⁺ T cell depletion did not significantly alter Mtb burden. Further analysis revealed that pulmonary CD8⁺ T cells from Mtb-infected CBA/J mice were clonally expanded, preferentially expressing T cell receptor (TcR) Vβ chain 8 (8.2, 8.3) or Vβ 14. Although Vβ8⁺ CD8⁺ T cells were responsible for the majority of IL-10 production, in vivo depletion of Vβ8⁺ did not significantly change the outcome of Mtb infection, which we hypothesize was a consequence of their dual IL-10/IFN-γ secreting profiles. Our data demonstrate that IL-10-secreting CD8⁺ T cells can arise during chronic Mtb infection, although the significance of this T cell population in tuberculosis pathogenesis remains unclear.     

Augmentation of effector CD8+ T cell generation with enhanced granzyme B expression by IL-27

IL-27 is a novel IL-12 family member that plays a role in the early regulation of Th1 initiation. We have recently demonstrated that IL-27 has a potent antitumor activity, which is mainly mediated through CD8+ T cells, and also has an adjuvant activity to induce epitope-specific CTL in vivo. In this study, we further investigated the in vitro effect of IL-27 on CD8+ T cells of mouse spleen cells. In a manner similar to CD4+ T cells, IL-27 activated STAT1, -2, -3, -4, and -5, and augmented the expression of T-bet, IL-12Rbeta2, and granzyme B, and slightly that of perforin in naive CD8+ T cells stimulated with anti-CD3. IL-27 induced synergistic IFN-gamma production with IL-12 and proliferation of naive CD8+ T cells. Moreover, IL-27 enhanced proliferation of CD4+ T cell-depleted spleen cells stimulated by allogeneic spleen cells and augmented the generation of CTL. In STAT1-deficient naive CD8+ T cells, IL-27-induced proliferation was not reduced, but synergistic IFN-gamma production with IL-12 was diminished with decreased expression of T-bet, IL-12Rbeta2, granzyme B, and perforin. In T-bet-deficient naive CD8+ T cells, IL-27-induced proliferation was hardly reduced, but synergistic IFN-gamma production with IL-12 was diminished with decreased expression of IL-12Rbeta2, granzyme B, and perforin. However, IL-27 still augmented the generation of CTL from T-bet-deficient CD4+ T cell-depleted spleen cells stimulated by allogeneic spleen cells with increased granzyme B expression. These results suggest that IL-27 directly acts on naive CD8+ T cells in T-bet-dependent and -independent manners and augments generation of CTL with enhanced granzyme B expression.     

Coordinate expression of CC chemokine ligand 5, granulysin, and perforin in CD8+ T cells provides a host defense mechanism against Mycobacterium tuberculosis

The ability of CD8+ T cells to kill intracellular pathogens depends upon their capacity to attract infected cells as well as their secretion of cytolytic and antimicrobial effector molecules. We examined the Ag-induced expression of three immune effector molecules contained within cytoplasmic granules of human CD8+ T cells: the chemokine CCL5, the cytolytic molecule perforin, and the antimicrobial protein granulysin. Macrophages infected with virulent Mycobacterium tuberculosis triggered the expression of CCL5 in CD8+ T cells only in donors with previous exposure to the tuberculosis bacteria, not in naive donors. Functionally, CCL5 efficiently attracted M. tuberculosis-infected macrophages, but failed to exert direct antibacterial activity. Infected macrophages also triggered the expression of granulysin in CD8+ T cells, and granulysin was found to be highly active against drug-susceptible and drug-resistant M. tuberculosis clinical isolates. The vast majority of CCL5-positive cells coexpressed granulysin and perforin. Taken together, this report provides evidence that a subset of CD8+ T cells coordinately expresses CCL5, perforin and granulysin, thereby providing a host mechanism to attract M. tuberculosis-infected macrophages and kill the intracellular pathogen.     

Normalization of Tumor Microenvironment by Neem Leaf Glycoprotein Potentiates Effector T Cell Functions and Therapeutically Intervenes in the Growth of Mouse Sarcoma

We have observed restriction of the murine sarcoma growth by therapeutic intervention of neem leaf glycoprotein (NLGP). In order to evaluate the mechanism of tumor growth restriction, here, we have analyzed tumor microenvironment (TME) from sarcoma bearing mice with NLGP therapy (NLGP-TME, in comparison to PBS-TME). Analysis of cytokine milieu within TME revealed IL-10, TGFβ, IL-6 rich type 2 characters was switched to type 1 microenvironment with dominance of IFNγ secretion within NLGP-TME. Proportion of CD8⁺ T cells was increased within NLGP-TME and these T cells were protected from TME-induced anergy by NLGP, as indicated by higher expression of pNFAT and inhibit related downstream signaling. Moreover, low expression of FasR⁺ cells within CD8⁺ T cell population denotes prevention from activation induced cell death. Using CFSE as a probe, better migration of T cells was noted within TME from NLGP treated mice than PBS cohort. CD8⁺ T cells isolated from NLGP-TME exhibited greater cytotoxicity to sarcoma cells in vitro and these cells show higher expression of cytotoxicity related molecules, perforin and granzyme B. Adoptive transfer of NLGP-TME exposed T cells, but not PBS-TME exposed cells in mice, is able to significantly inhibit the growth of sarcoma in vivo. Such tumor growth inhibition by NLGP-TME exposed T cells was not observed when mice were depleted for CD8⁺ T cells. Accumulated evidences strongly suggest NLGP mediated normalization of TME allows T cells to perform optimally to inhibit the tumor growth.     

Interleukin-4 impairs granzyme-mediated cytotoxicity of Simian virus 40 large tumor antigen-specific CTL in BALB/c mice

In this report we analyzed the impact of interleukin-4 (IL-4) on tumor-associated simian virus 40 (SV40) large T-antigen (TAg)-specific CD8⁺ cytotoxic T cells during rejection of syngeneic SV40 transformed mKSA tumor cells in BALB/c mice. Strikingly, challenge of naïve mice with low doses of mKSA tumor cells revealed a CD8⁺ T cell-dependent prolonged survival time of naïve IL-4^?/? mice. In mice immunized with SV40 TAg we observed in IL-4^?/? mice, or in wild type mice treated with neutralizing anti-IL-4 monoclonal antibody, a strongly enhanced TAg-specific cytotoxicity of tumor associated CD8⁺ T cells. The enhanced cytotoxicity in IL-4^?/? mice was accompanied by a significant increase in the fraction of CD8⁺ tumor associated T-cells expressing the cytotoxic effector molecules granzyme A and B and in granzyme B-specific enzymatic activity. The data suggest that endogenous IL-4 can suppress the generation of CD8⁺ CTL expressing cytotoxic effector molecules especially when the antigen induces only a very weak CTL response.     

CD4(+) and CD8(+) T cells kill intracellular Mycobacterium tuberculosis by a perforin and Fas/Fas ligand-independent mechanism

Cytotoxic effector phenotype and function of MHC-restricted Mycobacterium tuberculosis (MTB)-reactive CD4(+) and CD8(+) T lymphocytes were analyzed from healthy tuberculin skin test-positive persons. After stimulation in vitro with MTB, both CD4(+) and CD8(+) T cells up-regulated mRNA expression for granzyme A and B, granulysin, perforin, and CD95L (Fas ligand). mRNA levels for these molecules were greater for resting CD8(+) than CD4(+) T cells. After MTB stimulation, mRNA levels were similar for both T cell subsets. Increased perforin and granulysin protein expression was confirmed in both in CD4(+) and CD8(+) T cells by flow cytometry. Both T cell subsets lysed MTB-infected monocytes. Biochemical inhibition of the granule exocytosis pathway in CD4(+) and CD8(+) T cells decreased cytolytic function by >90% in both T cell subsets. Ab blockade of the CD95-CD95L interaction decreased cytolytic function for both T cell populations by 25%. CD4(+) and CD8(+) T cells inhibited growth of intracellular MTB in autologous monocytes by 74% and 84%, respectively. However, inhibition of perforin activity, the CD95-CD95L interaction, or both CTL mechanisms did not affect CD4(+) and CD8(+) T cell mediated restriction of MTB growth. Thus, perforin and CD95-CD95L were not involved in CD4(+) and CD8(+) T cell mediated restriction of MTB growth.     

Impairment of Vα24-Jα18+Vβ11+ natural killer T cells in adult acute lymphoblastic leukemia patients

Type I natural killer T (NKT) cells are attractive candidates for cancer immunotherapy. In this study, we examined the characteristics of type I NKT cells in patients with adult B-cell acute lymphoblastic leukemia (ALL). We first identified type I NKT cells as Vα24-Jα18 and Vβ11 double-positive CD3⁺ lymphocytes. Using this method, we found that the adult B-cell ALL patients presented significantly lower level of type I NKT cells than the age- and sex-matching control subjects. The expression of IL-21 by type I NKT cells was then examined using intracellular flow cytometry, which showed that with α-GalCer stimulation, the adult B-cell ALL patients presented significantly lower level of IL-21⁺ type I NKT cells than control subjects. By both flow cytometry and ELISA, we found that the vast majority of IL-21-expressing type I NKT cells expressed IL-21R, which was also reduced in adult B-cell ALL patients. Using an in vitro co-culture system, we demonstrated that IL-21R⁺, but not IL-21R^-, type I NKT cells could promote the IFN-γ, granzyme B, and perforin expression by CD8 T cells in an IL-21-dependent fashion. This type I NKT cell-mediated stimulatory effect was reduced in adult B-cell ALL patients than in control subjects. In addition, we observed a positive correlation between the frequency of IL-21R⁺ type I NKT cells and the frequencies of IFN-γ-, granzyme B-, and perforin-expressing circulating CD8 T cells in adult B-cell ALL patients directly ex vivo. Overall, this study identified an IL-21-related impairment in type I NKT cells from adult B-cell ALL patients.     

Perforin, granzyme B, and FasL expression by peripheral blood T lymphocytes in emphysema

Background

It is generally accepted that emphysematous lungs are characterized by an increase in the numbers of neutrophils, macrophages, and CD8⁺ T lymphocytes, the lasts having increased cytotoxic activity. Because systemic inflammation is also a component of emphysema, we hypothesize that peripheral CD8⁺ T lymphocytes of emphysematous smokers who show evidence of systemic inflammation will have higher expression of cytotoxic molecules.

Methods

We assessed parameters of systemic inflammation in normal individuals (smokers or non-smokers) and in emphysematous subjects with an active smoking history by measuring serum interleukine-6, C-reactive protein, and tumor necrosis factor. Expression of perforin, granzyme B, and FasL protein by CD8⁺ T lymphocytes, CD4⁺ T lymphocytes, and natural killer cells were assessed by flow cytometry while perforin, granzyme B, and FasL mRNA expression were measured on purified systemic CD8⁺ T lymphocytes by real-time PCR.

Results

Emphysematous smokers had higher levels of serum interleukine-6 than normal subjects. Even with the presence of systemic inflammation in emphysematous smokers, the percentage of peripheral CD8⁺ T lymphocytes, CD4⁺ T lymphocytes, and NK cells expressing perforin and granzyme B protein was not different between the three groups.

Conclusion

Despite evidence of systemic inflammation, peripheral T lymphocytes of emphysematous smokers did not show higher levels of cytotoxic markers, suggesting that increase of activated T lymphocytes in the emphysematous lung may be due to either activation in the lung or specific peripheral recruitment.     

Th17 and Th17-stimulated CD8<Superscript>+</Superscript> T cells play a distinct role in Th17-induced preventive and therapeutic antitumor immunity

CD4⁺ Th17 cells induce antitumor immunity leading to the eradication of established tumors. However, the mechanism of antitumour immunity and CTL activation by Th17 cells and the distinct role of Th17 and Th17-activated CTLs in antitumor immunity are still elusive. In this study, we generated ovalbumin (OVA)-specific Th17 cells by cultivating OVA-pulsed dendritic cells with CD4⁺ T cells derived from transgenic OTII mice in the presence of IL-6, IL-23, TGF-β, and anti-IFN-γ antibody. We demonstrated that Th17 cells acquired major histocompatibility complex/peptide (pMHC)-I and expressed RORγt, IL-17, and IL-2. Th17 cells did not have any direct in vitro tumor cell–killing activity. However, Th17 cells were able to stimulate CD8⁺ CTL responses via IL-2 and pMHC I, but not IL-17 signaling, which play a major role in Th17-induced preventive immunity against OVA-expressing B16 melanoma. Th17 cells stimulated the expression of CCL2 and CCL20 in lung tumor microenvironments promoting the recruitment of various inflammatory leukocytes (DCs, CD4⁺, and CD8⁺ T cells) stimulating more pronounced therapeutic immunity for early-stage (5-day lung metastases or 3 mm, s.c.) tumor than for well-established (6 mm, s.c.) tumor. The therapeutic effect of Th17 cells is associated with IL-17 and is mediated by Th17-stimulated CD8⁺ CTLs and other inflammatory leukocytes recruited into B16 melanoma via Th17-stimulated CCL20 chemoattraction. Taken together, our data elucidate a distinct role of Th17 and Th17-stimulated CD8⁺ CTLs in the induction of preventive and therapeutic antitumor immunity, which may greatly impact the development of Th17-based cancer immunotherapy.     

CD8+ T cells exhaustion induced by myeloid‐derived suppressor cells in myelodysplastic syndromes patients might be through TIM3/Gal‐9 pathway

CD8⁺ T cells play a central role in antitumour immunity, which often exhibit ‘exhaustion’ in the setting of malignancy and chronic viral infection due to T cell immunoglobulin and mucin domain 3 (TIM3) and myeloid‐derived suppressor cells (MDSCs). Our team previously found that overactive MDSCs and exhausted TIM3⁺CD8⁺ T cells were observed in myelodysplastic syndromes (MDS) patients. However, it is not obvious whether MDSCs suppress CD8⁺ T cells through TIM3/Gal‐9 pathway. Here, Gal‐9, as the ligand of TIM3, was overexpressed in MDSCs. The levels of Gal‐9 in bone marrow supernatants, serum and culture supernatants of MDSCs from MDS patients were elevated. CD8⁺ T cells from MDS or normal controls produced less perforin and granzyme B and exhibited increased early apoptosis after co‐culture with MDSCs from MDS. Meanwhile, the cytokines produced by CD8⁺ T cells could be partially restored by TIM3/Gal‐9 pathway inhibitors. Furthermore, CD8⁺ T cells produced less perforin and granzyme B after co‐culture with excess exogenous Gal‐9, and the function of CD8⁺ T cells was similarly restored by TIM3/Gal‐9 pathway inhibitors. Expression of Notch1, EOMES (associated with perforin and granzyme B secretion), p‐mTOR and p‐AKT (associated with cell proliferation) was decreased in CD8⁺ T cells from MDS after co‐culture with excess exogenous Gal‐9. These suggested that MDSCs might be the donor of Gal‐9, and TIM3/Gal‐9 pathway might be involved in CD8⁺ T cells exhaustion in MDS, and that TIM3/Gal‐9 pathway inhibitor might be the promising candidate for target therapy of MDS in the future.     

A lipopeptide facilitate induction of Mycobacterium leprae killing in host cells

Little is known of the direct microbicidal activity of T cells in leprosy, so a lipopeptide consisting of the N-terminal 13 amino acids lipopeptide (LipoK) of a 33-kD lipoprotein of Mycobacterium leprae, was synthesized. LipoK activated M. leprae infected human dendritic cells (DCs) to induce the production of IL-12. These activated DCs stimulated autologous CD4+ or CD8+ T cells towards type 1 immune response by inducing interferon-gamma secretion. T cell proliferation was also evident from the CFSE labeling of target CD4+ or CD8+ T cells. The direct microbicidal activity of T cells in the control of M. leprae multiplication is not well understood. The present study showed significant production of granulysin, granzyme B and perforin from these activated CD4+ and CD8+ T cells when stimulated with LipoK activated, M. leprae infected DCs. Assessment of the viability of M. leprae in DCs indicated LipoK mediated T cell-dependent killing of M. leprae. Remarkably, granulysin as well as granzyme B could directly kill M. leprae in vitro. Our results provide evidence that LipoK could facilitate M. leprae killing through the production of effector molecules granulysin and granzyme B in T cells.     

Altered effector function of peripheral cytotoxic cells in COPD

Background

There is mounting evidence that perforin and granzymes are important mediators in the lung destruction seen in COPD. We investigated the characteristics of the three main perforin and granzyme containing peripheral cells, namely CD8⁺ T lymphocytes, natural killer (NK; CD56⁺CD3^-) cells and NKT-like (CD56⁺CD3⁺) cells.

Methods

Peripheral blood mononuclear cells (PBMCs) were isolated and cell numbers and intracellular granzyme B and perforin were analysed by flow cytometry. Immunomagnetically selected CD8+ T lymphocytes, NK (CD56⁺CD3^-) and NKT-like (CD56⁺CD3⁺) cells were used in an LDH release assay to determine cytotoxicity and cytotoxic mechanisms were investigated by blocking perforin and granzyme B with relevant antibodies.

Results

The proportion of peripheral blood NKT-like (CD56⁺CD3⁺) cells in smokers with COPD (COPD subjects) was significantly lower (0.6%) than in healthy smokers (smokers) (2.8%, p < 0.001) and non-smoking healthy participants (HNS) (3.3%, p < 0.001). NK (CD56⁺CD3^-) cells from COPD subjects were significantly less cytotoxic than in smokers (16.8% vs 51.9% specific lysis, p < 0.001) as were NKT-like (CD56⁺CD3⁺) cells (16.7% vs 52.4% specific lysis, p < 0.001). Both cell types had lower proportions expressing both perforin and granzyme B. Blocking the action of perforin and granzyme B reduced the cytotoxic activity of NK (CD56⁺CD3^-) and NKT-like (CD56⁺CD3⁺) cells from smokers and HNS.

Conclusion

In this study, we show that the relative numbers of peripheral blood NK (CD56⁺CD3^-) and NKT-like (CD56⁺CD3⁺) cells in COPD subjects are reduced and that their cytotoxic effector function is defective.     

In Vivo Identification and Characterization of CD4+ Cytotoxic T Cells Induced by Virulent Brucella abortus Infection

CD4⁺ T cells display a variety of helper functions necessary for an efficient adaptive immune response against bacterial invaders. This work reports the in vivo identification and characterization of murine cytotoxic CD4⁺ T cells (CD4⁺ CTL) during Brucella abortus infection. These CD4⁺ CTLs express granzyme B and exhibit immunophenotypic features consistent with fully differentiated T cells. They express CD25, CD44, CD62L ,CD43 molecules at their surface and produce IFN-γ. Moreover, these cells express neither the co-stimulatory molecule CD27 nor the memory T cell marker CD127. We show here that CD4⁺ CTLs are capable of cytolytic action against Brucella-infected antigen presenting cells (APC) but not against Mycobacterium-infected APC. Cytotoxic CD4⁺ T cell population appears at early stages of the infection concomitantly with high levels of IFN-γ and granzyme B expression. CD4⁺ CTLs represent a so far uncharacterized immune cell sub-type triggered by early immune responses upon Brucella abortus infection.     

Synergy between interleukin-2 and prothymosin α for the increased generation of cytotoxic T lymphocytes against autologous human carcinomas

 Peripheral blood mononuclear cells (PBMC) from cancer patients were cultured in vitro with irradiated autologous tumor cells isolated from malignant effusions (mixed lymphocyte tumor cultures, MLTC) and low-dose (50 IU/ml) recombinant interleukin-2 (IL-2). The combination of IL-2 and prothymosin α (ProTα) resulted in a greater PBMC-induced response to the autologous tumor than that brought about by IL-2 alone. In particular, ProTα specifically enhanced the CD4⁺ T-cell-mediated proliferation against the autologous tumor. CD4⁺ T cells seemed to recognize tumor antigens presented by HLA-DR molecules expressed on the autologous monocytes, since preincubation of the latter with an anti-HLA-DR monoclonal antibody (mAb) abrogated the response. In addition, MLTC set up with IL-2 and ProTα also generated more MHC-class-I-restricted cytotoxic T lymphocytes (CTL) against the autologous tumor than did MLTC set up with IL-2 alone. The MLTC-induced CTL contained high levels of cytoplasmic perforin and their development was strictly dependent on the presence of both autologous CD4⁺ T cells and monocytes. In the absence of either population there was a strong impairment of both proliferative and cytotoxic responses which was not restored by the presence of ProTα. In contrast, when both cell populations were present, ProTα exerted optimal enhancement of CD4⁺ T cell proliferation, which was associated with potentiated CTL responses. Our data emphasize the role of ProTα for the enhancement of IL-2-induced CTL responses against autologous tumor cells. Such responses require collaborative interactions between CD4⁺, CD8⁺ T cells and monocytes as antigen-presenting cells. Our data are relevant for adoptive immunotherapeutic settings utilizing IL-2 and ProTα-induced autologous-tumor-specific CTL. Received: 2 March 2000 / Accepted: 1 June 2000     

Lung CD8+ T cells in COPD have increased expression of bacterial TLRs

Background

Toll-like receptors (TLRs) on T cells can modulate their responses, however, the extent and significance of TLR expression by lung T cells, NK cells, or NKT cells in chronic obstructive pulmonary disease (COPD) is unknown.

Methods

Lung tissue collected from clinically-indicated resections (n = 34) was used either: (a) to compare the expression of TLR1, TLR2, TLR2/1, TLR3, TLR4, TLR5, TLR6 and TLR9 on lung CD8+ T cells, CD4+ T cells, NK cells and NKT cells from smokers with or without COPD; or (b) to isolate CD8+ T cells for culture with anti-CD3ε without or with various TLR ligands. We measured protein expression of IFN-γ, TNF-α, IL-13, perforin, granzyme A, granzyme B, soluble FasL, CCL2, CCL3, CCL4, CCL5, CCL11, and CXCL9 in supernatants.

Results

All the lung subsets analyzed demonstrated low levels of specific TLR expression, but the percentage of CD8+ T cells expressing TLR1, TLR2, TLR4, TLR6 and TLR2/1 was significantly increased in COPD subjects relative to those without COPD. In contrast, from the same subjects, only TLR2/1 and TLR2 on lung CD4+ T cells and CD8+ NKT cells, respectively, showed a significant increase in COPD and there was no difference in TLR expression on lung CD56+ NK cells. Production of the Tc1 cytokines IFN-γ and TNF-α by lung CD8+ T cells were significantly increased via co-stimulation by Pam3CSK4, a specific TLR2/1 ligand, but not by other agonists. Furthermore, this increase in cytokine production was specific to lung CD8+ T cells from patients with COPD as compared to lung CD8+ T cells from smokers without COPD.

Conclusions

These data suggest that as lung function worsens in COPD, the auto-aggressive behavior of lung CD8+ T cells could increase in response to microbial TLR ligands, specifically ligands against TLR2/1.     

Maintenance of Intestinal Th17 Cells and Reduced Microbial Translocation in SIV-infected Rhesus Macaques Treated with Interleukin (IL)-21

In pathogenic HIV and SIV infections of humans and rhesus macaques (RMs), preferential depletion of CD4⁺ Th17 cells correlates with mucosal immune dysfunction and disease progression. Interleukin (IL)-21 promotes differentiation of Th17 cells, long-term maintenance of functional CD8⁺ T cells, and differentiation of memory B cells and antibody-secreting plasma cells. We hypothesized that administration of IL-21 will improve mucosal function in the context of pathogenic HIV/SIV infections. To test this hypothesis, we infected 12 RMs with SIV_mac239 and at day 14 post-infection treated six of them with rhesus rIL-21-IgFc. IL-21-treatment was safe and did not increase plasma viral load or systemic immune activation. Compared to untreated animals, IL-21-treated RMs showed (i) higher expression of perforin and granzyme B in total and SIV-specific CD8⁺ T cells and (ii) higher levels of intestinal Th17 cells. Remarkably, increased levels of Th17 cells were associated with reduced levels of intestinal T cell proliferation, microbial translocation and systemic activation/inflammation in the chronic infection. In conclusion, IL-21-treatment in SIV-infected RMs improved mucosal immune function through enhanced preservation of Th17 cells. Further preclinical studies of IL-21 may be warranted to test its potential use during chronic infection in conjunction with antiretroviral therapy.     

Ectonucleotidase CD38 Demarcates Regulatory,Memory-Like CD8+ T Cells with IFN-γ-Mediated Suppressor Activities

Regulatory CD8⁺ T cells are critical for self-tolerance and restricting excessive immune responses. The variety of immune functions they fulfill, the heterogeneity of their phenotype, and the mechanism of action are still poorly understood. Here we describe that regulatory CD8⁺ T cells exhibiting immunosuppressive actions in vitro and in vivo are recognized as CD38^high T cells and present in naive mice. CD38 is a glycosylated membrane protein with ectonucleotidase properties. CD8⁺CD38^high (CD44⁺CD122⁺CD62L^high) lymphocytes suppress CD4⁺ effector T-cell proliferation in an antigen-non specific manner via IFN-γ. While direct cell-to-cell contact is needed for this suppressor activity, it is independent of membrane-bound TGF-β and granzyme B release. IL-15 potentiates the suppressive activity of CD8⁺CD38^high T cells and controls their survival and expansion. In humans CD8⁺CD38^high T cells inhibit CD4⁺ effector T cell proliferation. In vivo, CD8⁺CD38^high, but not CD8⁺CD38⁻ T cells mitigate murine experimental autoimmune encephalomyelitis (EAE) by reducing the clinical score and delaying disease occurrence. EAE suppression is enhanced by pre-treatment of CD8⁺CD38^high T cells with IL-15. These findings add evidence that the expression of ectoenzyme receptor family members positively correlates with suppressor functions and identifies CD8⁺CD38^high T cells as potential inhibitors of excessive immune responses.     

Role of perforin, granzymes and the proliferative state of the target cells in apoptosis and necrosis mediated by bispecific-antibody-activated cytotoxic T cells

 Bispecific monoclonal antibodies (bi-mAb), directed against a tumor-associated antigen and the CD3 or CD28 antigen on T lymphocytes, induce activation of resting T lymphocytes and target-specific tumor cell lysis. We now show that both necrosis and apoptosis contribute to T-cell-mediated tumor cell destruction. Even though T cells up-regulate FAS/APO-1 expression upon bi-mAb stimulation, FAS/APO-1-mediated apoptosis does not contribute to bi-mAb-mediated destruction of Hodgkin’s cells. CD8⁺ lymphocytes were the most potent effectors of bi-mAb-mediated cytotoxicity and had the highest levels of mRNA coding for perforin and granzyme A and B. Ca²⁺-complexing agents, which abrogate perforin activity, led to decreased levels of necrosis, while inhibition of granzyme activity in effector or target cells had a similar effect on apoptosis. Granzyme-mediated apoptosis critically dependent on the proliferative state of the target cells, while perforin-induced necrosis was not cell-cycle-dependent. Our results underline the importance of the expression levels of perforin and granzymes in the effector T cells and of the proliferative state of the target cells in bi-mAb-mediated apoptosis and necrosis of tumor cells. Received: 5 December 1996 / Accepted: 16 January 1997