Cross-Differentiation from the CD8 Lineage to CD4 T Cells in the Gut-Associated Microenvironment with a Nonessential Role of Microbiota

SummaryCD4 and CD8 T cell lineages differentiate through respective thymic selection processes. Here, we report cross-differentiation from the CD8 lineage to CD4 T cells, but not vice versa, predominantly in the large-intestine-associated microenvironment. It occurred in the absence or distal presence of cognate antigens. This pathway produced MHC-class-I-restricted CD4+Foxp3+ Treg (CI-Treg) cells. Blocking T cell-intrinsic TGFβ signaling diminished CI-Treg populations in lamina propria, but it did not preclude the CD8-to-CD4 conversion. Microbiota were not required for the cross-differentiation, but the presence of microbiota led to expansion of the converted CD4 T cell population in the large intestine. CI-Treg cells did not promote tolerance to microbiota per se, but they regulated systemic homeostasis of T lymphocytes and protected the large intestine from inflammatory damage. Overall, the clonal conversion from the CD8 lineage to CD4 T cell subsets occurred regardless of “self” or “nonself.” This lineage plasticity may promote “selfless” tolerance for immune balance

New Insights into the Generation of CD4 Memory May Shape Future Vaccine Strategies for Influenza

Influenza viral evolution presents a formidable challenge to vaccination due to the virus\u27 ability to rapidly mutate to evade immune responses. Live influenza infections generate large and diverse CD4 effector T cell responses that yield highly protective, long-lasting CD4 T cell memory that can target conserved viral epitopes. We review advances in our understanding of mechanisms involved in generating CD4 T cell responses against the influenza A virus (IAV), focusing on specialized follicular helper (TFH) and CD4 cytotoxic (ThCTL) effector subsets and on CD4 T cell memory. We also discuss two recent findings in context of enhancing vaccine responses. First, helper T cells require priming with APC secreting high levels of IL-6. Second, the transition of IAV-generated effectors to memory depends on IL-2, costimulation and antigen signals, just before effectors reach peak numbers, defined as the memory checkpoint. The need for these signals during the checkpoint could explain why many current influenza vaccines are poorly effective and elicit poor cellular immunity. We suggest that CD4 memory generation can be enhanced by re-vaccinating at this time. Our best hope lies in a universal vaccine that will not need to be formulated yearly against seasonal antigenically novel influenza strains and will also be protective against a pandemic strain. We suggest a vaccine approach that elicits a powerful T cell response, by initially inducing high levels of APC activation and later providing antigen at the memory checkpoint, may take us a step closer to such a universal influenza vaccine

CD4 Effectors Need to Recognize Antigen Locally to Become Cytotoxic CD4 and Follicular Helper T Cells [preprint]

T follicular helper (TFH) and Cytotoxic CD4 (ThCTL) are tissue-restricted CD4 effector subsets, functionally specialized to mediate optimal Ab production and cytotoxicity of infected cells. Influenza infection generates robust CD4 responses, including lung ThCTL and SLO TFH, that protect against reinfection by variant strains. Antigen (Ag) presentation after infection, lasts through the effector phase of the response. Here, we show that this effector phase Ag presentation, well after priming, is required to drive CD4 effectors to ThCTL and TFH. Using in vivo influenza models, we varied Ag presentation to effectors acutely, just at the effector phase. Ag presentation was required in the tissue of effector residence. We suggest these requirements contain unnecessary or potentially pathogenic CD4 responses, only allowing them if infection is uncleared. The results imply that providing effector phase Ag, would lead to stronger humoral and CD4 tissue immunity and thus can be applied to improve vaccine design

Regulation of CD4+ Autoimmune Memory by CTLA4

Immunological memory is a hallmark of adaptive immunity, a defense mechanism endowed to vertebrates during evolution. However, an autoimmune pathogenic role of memory lymphocytes is also emerging with accumulating evidence. It is conceivable that autoimmune memory would be particularly harmful since memory cells would “constantly remember” and attack the body’s healthy tissues. It is even more detrimental given the resistance of memory T cells to immunomodulatory therapies. On the other hand, with their long-lasting potency the autoimmune memory cells could also play a critical role in anti-tumor immunity, which may be largely based on their reactivity to self-antigens. In this dissertation, I will discuss the role of autoimmune CD4+ effector memory T cells (TEM) in chronic and acute infectious disease settings while presenting to you evidence on their pathogenicity in autoimmune disease. Quantitative variations in CTLA4 expression, due to genetic polymorphisms, are associated with various human autoimmune conditions, including type 1 diabetes (T1D). Extensive studies have demonstrated that CTLA4 is not only essential for the suppressive role of regulatory T (Treg) cells, but also required for intrinsic control of conventional T (Tconv) cells. We report that a modest insufficiency of CTLA4 in mice, which mimics the effect of some human CTLA4 genetic polymorphisms, accompanied by a T1D-permissive MHC locus, was sufficient to induce juvenile-onset diabetes on an otherwise T1D-resistant genetic background. Reduction in CTLA4 levels had an unanticipated effect in promoting Treg cell function both in vivo and in vitro. This cell-intrinsic impact of CTLA4 reduction in Treg cells led to an increase in Treg memory in both lymphoid and nonlymphoid target tissue. Conversely, modulating CTLA4 by either RNAi or antibody blockade promoted TEM formation in the Tconv compartment. The CD4+ TEM cells, including those within target tissue, produced IL17 or IFNγ. Blocking IL7 signaling reduced the Th17 autoimmune compartment, but did not suppress the T1D induced by CTLA4 insufficiency. Enhanced effector memory formation in both Tconv and Treg lineages may underpin the apparently dichotomized impact of CTLA4 insufficiency on autoimmune pathogenesis. Therefore, while the presence of CTLA4 plays a critical role in controlling homeostasis of T cells, its quantitative variation may impose diverse or even opposing effects on distinct lineages of T cells, an optimal sum of which is necessary for preservation of T-cell immunity while suppressing tissue damage. Variations in CTLA4 splicing have been implicated in several gene polymorphisms that increase susceptibility to T1D. We established an in-vitro system to study the effects of reduction in specific splice variants levels of CTLA4, using lentiviral RNAi technology, in human T cells. There was an increased proliferation of CD4+ T cells on a reduction in the ¼CTLA4 splice variant akin to the effects caused by a reduction in sCTLA4 (soluble CTLA4) and FlCTLA4 (full-length CTLA4) splice variants. This data is intriguing in light of the recently published study that suggests that the functions of ¼CTLA4 are opposite to that of FlCTLA4 and sCTLA4. This system generated interesting preliminary data and has the potential to be used further to explore a number of questions pertaining to the role of CTLA4 splice variants with physiological relevance to T cell responses in human disease.</p

The immunological identity of tumor

By means of well-characterized autoimmunity models, we comparatively probed the “selfness” of malignant cells and their normal counterparts. We found that tumors activate self-tolerance mechanisms much more efficiently than normal tissues, reflecting a status of immunoprivileged “self.” Our findings indicate that potent autoimmune responses can eradicate established malignancies, yet the collateral destruction of healthy tissues may prove difficult to circumvent

Opposing effects of CTLA4 insufficiency on regulatory versus conventional T cells in autoimmunity converge on effector memory in target tissue

Quantitative variations in CTLA4 expression, because of genetic polymorphisms, are associated with various human autoimmune conditions, including type 1 diabetes (T1D). Extensive studies have demonstrated that CTLA4 is not only essential for the suppressive role of regulatory T cells (T(reg)) but also required for intrinsic control of conventional T (T(conv)) cells. We report that a modest insufficiency of CTLA4 in mice, which mimics the effect of some human CTLA4 genetic polymorphisms, accompanied by a T1D-permissive MHC locus, was sufficient to induce juvenile-onset diabetes on an otherwise T1D-resistant genetic background. Reduction in CTLA4 levels had an unanticipated effect in promoting Treg function both in vivo and in vitro. It led to an increase in T(reg) memory in both lymphoid and nonlymphoid target tissue. Conversely, modulating CTLA4 by either RNA interference or Ab blockade promoted conventional effector memory T cell formation in the T(conv) compartment. The CD4(+) conventional effector memory T cells, including those within target tissue, produced IL-17 or IFN-γ. Blocking IL-7 signaling reduced the Th17 autoimmune compartment but did not suppress the T1D induced by CTLA4 insufficiency. Enhanced effector memory formation in both T(conv) and T(reg) lineages may underpin the apparently dichotomized impact of CTLA4 insufficiency on autoimmune pathogenesis. Therefore, although the presence of CTLA4 plays a critical role in controlling homeostasis of T cells, its quantitative variation may impose diverse or even opposing effects on distinct lineages of T cells, an optimal sum of which is necessary for preservation of T cell immunity while suppressing tissue damage

New Insights Into The Generation Of Cd4 Memory May Shape Future Vaccine Strategies For Influenza

Influenza viral evolution presents a formidable challenge to vaccination due to the virus\u27 ability to rapidly mutate to evade immune responses. Live influenza infections generate large and diverse CD4 effector T cell responses that yield highly protective, long-lasting CD4 T cell memory that can target conserved viral epitopes. We review advances in our understanding of mechanisms involved in generating CD4 T cell responses against the influenza A virus (IAV), focusing on specialized follicular helper (TFH) and CD4 cytotoxic (ThCTL) effector subsets and on CD4 T cell memory. We also discuss two recent findings in context of enhancing vaccine responses. First, helper T cells require priming with APC secreting high levels of IL-6. Second, the transition of IAV-generated effectors to memory depends on IL-2, costimulation and antigen signals, just before effectors reach peak numbers, defined as the memory checkpoint. The need for these signals during the checkpoint could explain why many current influenza vaccines are poorly effective and elicit poor cellular immunity. We suggest that CD4 memory generation can be enhanced by re-vaccinating at this time. Our best hope lies in a universal vaccine that will not need to be formulated yearly against seasonal antigenically novel influenza strains and will also be protective against a pandemic strain. We suggest a vaccine approach that elicits a powerful T cell response, by initially inducing high levels of APC activation and later providing antigen at the memory checkpoint, may take us a step closer to such a universal influenza vaccine

Short-Lived Antigen Recognition But Not Viral Infection At A Defined Checkpoint Programs Effector Cd4 T Cells To Become Protective Memory

Although memory CD4 T cells are critical for effective immunity to pathogens, the mechanisms underlying their generation are still poorly defined.We find that following murine influenza infection, most effector CD4 T cells undergo apoptosis unless they encounter cognate Ag at a defined stage near the peak of effector generation. Ag recognition at this memory checkpoint blocks default apoptosis and programs their transition to long-lived memory. Strikingly, we find that viral infection is not required, because memory formation can be restored by the addition of short-lived, Ag-pulsed APC at this checkpoint. The resulting memory CD4 T cells express an enhanced memory phenotype, have increased cytokine production, and provide protection against lethal influenza infection. Finally, we find that memory CD4 T cell formation following cold-adapted influenza vaccination is boosted when Ag is administered during this checkpoint. These findings imply that persistence of viral Ag presentation into the effector phase is the key factor that determines the efficiency of memory generation. We also suggest that administering Ag at this checkpoint may improve vaccine efficacy

Pathogen Recognition by CD4 Effectors Drives Key Effector and Most Memory Cell Generation Against Respiratory Virus

Although much is known about the mechanisms by which pathogen recognition drives the initiation of T cell responses, including those to respiratory viruses, the role of pathogen recognition in fate decisions of T cells once they have become effectors remains poorly defined. Here, we review our recent studies that suggest that the generation of CD4 T cell memory is determined by recognition of virus at an effector “checkpoint.” We propose this is also true of more highly differentiated tissue-restricted effector cells, including cytotoxic “ThCTL” in the site of infection and TFH in secondary lymphoid organs. We point out that ThCTL are key contributors to direct viral clearance and TFH to effective Ab response, suggesting that the most protective immunity to influenza, and by analogy to other respiratory viruses, requires prolonged exposure to antigen and to infection-associated signals. We point out that many vaccines used today do not provide such prolonged signals and suggest this contributes to their limited effectiveness. We also discuss how aging impacts effective CD4 T cell responses and how new insights about the response of aged naive CD4 T cells and B cells might hold implications for effective vaccine design for both the young and aged against respiratory viruses