Acute Symptomatic Influenza A Virus (IAV) Infection in Humans Leads to Expansion of Highly Diverse CD8 T Cell Repertoires Crossreactive with Persistent Epstein Barr Virus (EBV)

The competence of T cell responses predominantly depends on how efficient T cell receptors (TCRs) are at recognizing antigenic epitopes. We show here that during acute severely symptomatic IAV infection there was an expansion of IAV-M1/EBV-BRLF1 and IAV-M1/EBV-BMLF1 double-tetramer+ cells directly ex-vivo in 5 HLA-A2+ patients. We questioned whether this expansion specific to these two different crossreactive responses would lead to alterations in the TCR repertoire of the IAV-M158 , EBV-BRLF1109 and -BMLF1280 from before, during and following acute IAV infection. Using staining with Vb MAb we found that T cell responses generated to these epitopes became surprisingly more polyclonal, with the sharing of Vb between M1, BMLF1 and BRLF1 populations which is not seen in healthy donors and which decreased 2 months later consistent with crossreactive expansion. Furthermore, by using single-cell analysis of TCRα and TCRβ repertoire of tetramer sorted IAV-M1 cells we showed dramatic changes in specific clonotype usage and in JA and JB family usage during acute IAV infection compared to before infection. In summary, these changes in TCR repertoire during acute symptomatic IAV infection suggest that during severe infection there is a preferential expansion of highly diverse crossreactive responses between IAV and the persistent virus, EBV, which leads to permanent changes in TCR repertoires to both of these two viruses. (NIHAI49320)

T cells in the brain enhance neonatal mortality during peripheral LCMV infection

In adult mice the severity of disease from viral infections is determined by the balance between the efficiency of the immune response and the magnitude of viral load. Here, the impact of this dynamic is examined in neonates. Newborns are highly susceptible to infections due to poor innate responses, lower numbers of T cells and Th2-prone immune responses. Eighty-percent of 7-day old mice, immunologically equivalent to human neonates, succumbed to extremely low doses (5 PFU) of the essentially non-lethal lymphocytic choriomeningitis virus (LCMV-Armstrong) given intraperitoneally. This increased lethality was determined to be dependent upon poor early viral control, as well as, T cells and perforin as assessed in knockout mice. By day 3, these neonatal mice had 400-fold higher viral loads as compared to adults receiving a 10,000-fold (5X104 PFU) higher dose of LCMV. The high viral load in combination with the subsequent immunological defect of partial CD8 T cell clonal exhaustion in the periphery led to viral entry and replication in the brain. Within the brain, CD8 T cells were protected from exhaustion, and thus were able to mediate lethal immunopathology. To further delineate the role of early viral control, neonatal mice were infected with Pichinde virus, a less virulent arenavirus, or LCMV was given to pups of LCMV-immune mothers. In both cases, peak viral load was at least 29-fold lower, leading to functional CD8 T cell responses and 100% survival

Severity of Infectious Mononucleosis (IM) Correlates with the Frequency of Crossreactive Influenza A Virus (IAV)-M1 and Epstein Barr Virus (EBV)-BMLF-1-specific CD8 T Cells

During EBV-associated IM IAV-specific crossreactive memory T cells are activated and play a role in disease severity. In HLA-A2+ IM patients, influenza M158 (IAV-M1)-specific CD8 memory T cell responses crossreacted with two different EBV lytic epitopes, BMLF1280 (17/29) and BRLF1190 (19/20). Furthermore, 11/22 IM patients demonstrated some intra-viral crossreactivity between EBV-BRLF1 and -BMLF1 responses. Disease severity of IM directly correlated with significantly increased frequencies of crossreactive IAV-M1/EBV-BMLF1, IAV-M1, and EBV-BMLF1 specific CD8 cells, and with mean viral load over the first 5 weeks of infection. Disease severity did not correlate with BRLF1 or M1/BRLF1 crossreactive responses. When severity of IM was scored and patients were assigned to either mild or severe groups, disease severity correlated with specific TCR Vb usage in IAV-M1 population suggesting that TcR selection is driving disease outcome. Consistent with IAV-M1 and EBV-BMLF1 responses driving increased immunopathology was the observation that patients with severe disease had significantly more IAV-M1 and EBV-BMLF1 cells producing IFNg/MIP1-b in response to antigen as compared to patients with mild disease. These results suggest that T cell crossreactivity impacts T cell selection and function and ultimately disease outcome. Insights on these issues are important for the intelligent design of vaccines and to develop therapeutic interventions for virally induced disease (NIHAI49320)

Protective Heterologous Antiviral Immunity and Enhanced Immunopathogenesis Mediated by Memory T Cell Populations

A basic principle of immunology is that prior immunity results in complete protection against a homologous agent. In this study, we show that memory T cells specific to unrelated viruses may alter the host's primary immune response to a second virus. Studies with a panel of heterologous viruses, including lymphocytic choriomeningitis (LCMV), Pichinde (PV), vaccinia (VV), and murine cytomegalo (MCMV) viruses showed that prior immunity with one of these viruses in many cases enhanced clearance of a second unrelated virus early in infection. Such protective immunity was common, but it depended on the virus sequence and was not necessarily reciprocal. Cell transfer studies showed that both CD4 and CD8 T cell populations from LCMV-immune mice were required to transfer protective immunity to naive hosts challenged with PV or VV. In the case of LCMV-immune versus naive mice challenged with VV, there was an enhanced early recruitment of memory phenotype interferon (IFN) γ–secreting CD4+ and CD8+ cells into the peritoneal cavity and increased IFN-γ levels in this initial site of virus replication. Studies with IFN-γ receptor knockout mice confirmed a role for IFN-γ in mediating the protective effect by LCMV-immune T cell populations when mice were challenged with VV but not PV. In some virus sequences memory cell populations, although clearing the challenge virus more rapidly, elicited enhanced IFN-γ–dependent immunopathogenesis in the form of acute fatty necrosis. These results indicate that how a host responds to an infectious agent is a function of its history of previous infections and their influence on the memory T cell pool

PC61 (anti-CD25) treatment inhibits influenza A virus-expanded regulatory T cells and severe lung pathology during a subsequent heterologous lymphocytic choriomeningitis virus infection

Prior immunity to influenza A virus (IAV) in mice changes the outcome to a subsequent lymphocytic choriomeningitis virus (LCMV) infection and can result in severe lung pathology, similar to that observed in patients that died of the 1918 H1N1 pandemic. This pathology is induced by IAV-specific memory CD8(+) T cells cross-reactive with LCMV. Here, we discovered that IAV-immune mice have enhanced CD4(+) Foxp3(+) T-regulatory (Treg) cells in their lungs, leading us to question whether a modulation in the normal balance of Treg and effector T-cell responses also contributes to enhancing lung pathology upon LCMV infection of IAV-immune mice. Treg cell and interleukin-10 (IL-10) levels remained elevated in the lungs and mediastinal lymph nodes (mLNs) throughout the acute LCMV response of IAV-immune mice. PC61 treatment, used to decrease Treg cell levels, did not change LCMV titers but resulted in a surprising decrease in lung pathology upon LCMV infection in IAV-immune but not in naive mice. Associated with this decrease in pathology was a retention of Treg in the mLN and an unexpected partial clonal exhaustion of LCMV-specific CD8(+) T-cell responses only in IAV-immune mice. PC61 treatment did not affect cross-reactive memory CD8(+) T-cell proliferation. These results suggest that in the absence of IAV-expanded Treg cells and in the presence of cross-reactive memory, the LCMV-specific response was overstimulated and became partially exhausted, resulting in a decreased effector response. These studies suggest that Treg cells generated during past infections can influence the characteristics of effector T-cell responses and immunopathology during subsequent heterologous infections. Thus, in humans with complex infection histories, PC61 treatment may lead to unexpected results

Crossreactive Epstein-Barr Virus (EBV)-Influenza A Virus (IAV) Specific CD8 Memory T Cells During Acute Symptomatic IAV Infection

We previously showed that crossreactivity is common between IAV and EBV in HLA-A2+ patients during infectious mononucleosis. IAV-M1-GIL58-66 specific CD8 T cells, along with expanded populations of IAV-M1-GIL58-66/EBV-BRLF-1109-117 -YVL and IAV-M1-GIL58-66/EBV-BMLF1280-288-GLC double-tetramer+ cells were detected directly ex-vivo in 5 HLA-A2+ patients. Altered IAV-M158-66, EBV-BRLF1119-117 and -BMLF1280-288 TCR repertoires were observed over the course of infection and in comparison to healthy donors. After culture, cells were sorted and analyzed by gene array in order to assess global changes in immune responses following different stimulations, either cognate or crossreactive, in different patient populations. M1-GIL and BRLF1-YVL specific cells had similar immune-response gene signatures, but the -GLC specific CD8 cells were more similar to the two-crossreactive populations. Crossreactive M1-GIL/BRLF1-YVL cells from the BRLF1-YVL line were different in their activation status than the BRLF1-specific cells, consistent with BRLF1-YVL ligand stimulation of different gene activation profiles in these two populations. These results suggest that during symptomatic IAV infection there is an expansion of EBV/IAV crossreactive memory CD8 T cell responses. Ongoing studies are investigating whether EBV-IAV cross-reactive CD8+ T cells may contribute to immunopathology during acute IAV infection (NIH / NIAID PO1 AI 049320)

Epstein-Barr Virus (EBV)-lytic Cross-reactive Influenza-A (IAV) Memory CD8 T-cells in EBV Sero-negative Middle-aged Adults

EBV is a common human pathogen, which infects ~90% of people and establishes a life-long chronic infection. The clinical outcomes of acute infection can range from asymptomatic to severe immunopathology such as infectious mononucleosis (IM). However, for unknown reasons 5-10% of middle-aged adults (\u3e35 years) remain EBV-seronegative (EBV-SN) when the virus infects the vast majority of people, and is actively shed at high titers during chronic infection. Here we show that EBV-SN (ASN) HLA-A2+ middle-aged adults possess a unique IAV-M1-GIL58-66 memory CD8 T-cell response that cross-reacts with EBV lytic epitopes that differs from teenage EBV-SN (TSN) (18-19 years) and EBV-seropositive (EBV-SP) adult donors. The five tested HLA-A2+ EBV-SN middle-aged adults had a significantly increased IAV-M158-66-GIL tetramer+ CD8 frequency compared to EBV-SP donors. Upon exposure to EBV antigens in vitro both IAV-M158-66GIL/EBV-BMLF1280-288-GLC and IAV-M158-66-GIL/EBV-BRLF1109-117-YVL, functionally cross-reactive CD8+ responses could be detected in the peripheral blood of middle-aged EBV-SN donors, while only IAV-M1/EBV-YVL cross-reactive responses were detected in some teenage EBV-SN or EBV-seropositive people . Surprisingly, these IAV-M1-GIL-specific CD8 T-cells in middle-aged EBV-SN adults expanded dramatically to EBV lytic antigens and produced cytokines at high functional avidity. They lysed EBV-infected targets and showed potential (by CD103 expression) to enter mucosal epithelial tissue where infection initiates. Additionally, these cross-reactive cells had an oligo-clonal T-cell receptor repertoire different than EBV-SP donors. Taken together these data suggest that an altered cross-reactive T cell repertoire could mediate protective immunity against viral infection. Our results imply that sero-negative adults might have the ability to resist viral infection via heterologous immunity. (NIH-AI49320)

Private specificities of CD8 T cell responses control patterns of heterologous immunity

CD8 T cell cross-reactivity between viruses can play roles in protective heterologous immunity and damaging immunopathology. This cross-reactivity is sometimes predictable, such as between lymphocytic choriomeningitis virus (LCMV) and Pichinde virus, where cross-reactive epitopes share six out of eight amino acids. Here, however, we demonstrate more subtle and less predictable cross-reactivity between LCMV and the unrelated vaccinia virus (VV). Epitope-specific T cell receptor usage differed between individual LCMV-infected C57BL/6 mice, even though the mice had similar epitope-specific T cell hierarchies. LCMV-immune mice challenged with VV showed variations, albeit in a distinct hierarchy, in proliferative expansions of and down-regulation of IL-7Rα by T cells specific to different LCMV epitopes. T cell responses to a VV-encoded epitope that is cross-reactive with LCMV fluctuated greatly in VV-infected LCMV-immune mice. Adoptive transfers of splenocytes from individual LCMV-immune donors resulted in nearly identical VV-induced responses in each of several recipients, but responses differed depending on the donor. This indicates that the specificities of T cell responses that are not shared between individuals may influence cross-reactivity with other antigens and play roles in heterologous immunity upon encounter with another pathogen. This variability in cross-reactive T cell expansion that is unique to the individual may underlie variation in the pathogenesis of infectious diseases

Epstein-Barr Virus Epitope-Major Histocompatibility Complex Interaction Combined with Convergent Recombination Drives Selection of Diverse T Cell Receptor alpha and beta Repertoires

Recognition modes of individual T cell receptors (TCRs) are well studied, but factors driving the selection of TCR repertoires from primary through persistent human virus infections are less well understood. Using deep sequencing, we demonstrate a high degree of diversity of Epstein-Barr virus (EBV)-specific clonotypes in acute infectious mononucleosis (AIM). Only 9% of unique clonotypes detected in AIM persisted into convalescence; the majority (91%) of unique clonotypes detected in AIM were not detected in convalescence and were seeming replaced by equally diverse de novo clonotypes. The persistent clonotypes had a greater probability of being generated than nonpersistent clonotypes due to convergence recombination of multiple nucleotide sequences to encode the same amino acid sequence, as well as the use of shorter complementarity-determining regions 3 (CDR3s) with fewer nucleotide additions (i.e., sequences closer to germ line). Moreover, the two most immunodominant HLA-A2-restricted EBV epitopes, BRLF1109 and BMLF1280, show highly distinct antigen-specific public (i.e., shared between individuals) features. In fact, TCRalpha CDR3 motifs played a dominant role, while TCRbeta played a minimal role, in the selection of TCR repertoire to an immunodominant EBV epitope, BRLF1. This contrasts with the majority of previously reported repertoires, which appear to be selected either on TCRbeta CDR3 interactions with peptide/major histocompatibility complex (MHC) or in combination with TCRalpha CDR3. Understanding of how TCR-peptide-MHC complex interactions drive repertoire selection can be used to develop optimal strategies for vaccine design or generation of appropriate adoptive immunotherapies for viral infections in transplant settings or for cancer. IMPORTANCE Several lines of evidence suggest that TCRalpha and TCRbeta repertoires play a role in disease outcomes and treatment strategies during viral infections in transplant patients and in cancer and autoimmune disease therapy. Our data suggest that it is essential that we understand the basic principles of how to drive optimum repertoires for both TCR chains, alpha and beta. We address this important issue by characterizing the CD8 TCR repertoire to a common persistent human viral infection (EBV), which is controlled by appropriate CD8 T cell responses. The ultimate goal would be to determine if the individuals who are infected asymptomatically develop a different TCR repertoire than those that develop the immunopathology of AIM. Here, we begin by doing an in-depth characterization of both CD8 T cell TCRalpha and TCRbeta repertoires to two immunodominant EBV epitopes over the course of AIM, identifying potential factors that may be driving their selection