Over the past five years or so, there has been an accumulation of evidence demonstrating that not all pathogen-specific T cells are created equal. In particular, HIV-specific T cells that are capable of multiple functions have been shown to correlate more reliably with control of HIV replication and long term non progression than HIV-specific T cells with a more limited range of capabilities, such as the production of the cytokine interferon gamma alone. This was first demonstrated in 2002 by Mark Boaz and colleagues looking at HIV-specific CD4 T cells that could make IL-2 in addition to interferon gamma. Since then, the use of a technique called multi-parameter flow cytometry has allowed researchers to measure multiple T cell functions simultaneously. Researchers from the NIH’s Vaccine Research Center (VRC) have developed this technique by homing in on five potentially important functions: the production of the cytokines IL-2, TNF-alpha, interferon gamma and the chemokine MIP1-beta along with expression of a cell surface marker called CD107a (expression of this marker has been shown to correlate with the ability of T cells to efficiently kill infected cells). The VRC’s work has shown that having a higher proportion of HIV-specific T cells capable of performing four or five of these functions simultaneously is associated with non-progressive HIV infection. Recent VRC data also indicates that immunization with vaccinia virus – a highly successful vaccine against smallpox – elicits polyfunctional CD8 T cells, suggesting that they may be an important correlate of immunity.
The VRC has now collaborated with Robert Seder at NIAID to study multifunctional CD4 T cell responses in the mouse model of leishmania major infection. The research, just published in the advance online section of Nature Medicine, shows that the frequency of leishmania-specific CD4 T cells capable of simultaneously producing interferon gamma, IL-2 and TNF-alpha predicts the degree of protection obtained with vaccination. The authors conclude that “the quality of a CD4 T-cell cytokine response can be a crucial determinant in whether a vaccine is protective.” The authors also report that multifunctional CD4 T cells produce far more interferon gamma on a per-cell basis than CD4 T cells of more limited functionality; the same finding was recently reported by Rama Rao Amara and colleagues from the Emory University in the advance online section of J. Virology.
Published online: 10 June 2007 | doi:10.1038/nm1592
Patricia A Darrah, Dipti T Patel, Paula M De Luca, Ross W B Lindsay, Dylan F Davey, Barbara J Flynn, Søren T Hoff, Peter Andersen, Steven G Reed, Sheldon L Morris, Mario Roederer & Robert A Seder
CD4+ T cells have a crucial role in mediating protection against a variety of pathogens through production of specific cytokines. However, substantial heterogeneity in CD4+ T-cell cytokine responses has limited the ability to define an immune correlate of protection after vaccination. Here, using multiparameter flow cytometry to assess the immune responses after immunization, we show that the degree of protection against Leishmania major infection in mice is predicted by the frequency of CD4+ T cells simultaneously producing interferon-gamma, interleukin-2 and tumor necrosis factor. Notably, multifunctional effector cells generated by all vaccines tested are unique in their capacity to produce high amounts of interferon-gamma. These data show that the quality of a CD4+ T-cell cytokine response can be a crucial determinant in whether a vaccine is protective, and may provide a new and useful prospective immune correlate of protection for vaccines based on T-helper type 1 (TH1) cells.
J Virol. 2007 Jun 6; [Epub ahead of print]
Kannanganat S, Ibegbu C, Chennareddi L, Robinson HL, Amara RR.
Virus-specific CD4 T cells are endowed with multiple functions such as cytokine production, CD40L expression (co-stimulation for CD8 and B cells) and degranulation (cytotoxic potential). Here, we use anti-viral CD4 T cells present in human blood to evaluate the relationship between cytokine production and other functions of CD4 T cells. Anti-viral CD4 T cells for a persistent infection, cytomegalovirus (CMV) and two non-persistent infections, influenza virus (flu) and the smallpox vaccine (vaccinia virus), were studied. CD4 T cells for each of the infections produced all 7 possible cytokine co-expression subsets of IFN-gamma, IL-2 and TNF-alpha. Cells producing three or two cytokines (triple producers and double producers) represented nearly 50% of the total response for each of the infections. Triple producers expressed the highest levels of cytokines per cell; and single producers, the lowest. Following stimulation, higher frequencies of triple producers than single producers expressed CD40L. Only CMV-specific CD4 T cells underwent degranulation. However, higher frequencies of CMV-specific triple producers than single producers showed this functional characteristic. In contrast to the functional phenotypes, triple producers did not differ from IFN-gamma single producers for the memory phenotype. These results demonstrate a strong positive association between the cytokine co-production capacity of a virus-specific CD4 T cell and its other functional characteristics and suggest that vaccines should aim to elicit T cells that co-produce more than one cytokine.