The early work of the Clinical and Molecular Retrovirology Section involved studies aimed at dissecting the normal immunoregulatory mechanisms that control the human immune response to specific antigen challenges. When the AIDS epidemic emerged, H. Clifford Lane, M.D., became one of the first investigators to study immunopathogenic mechanisms of HIV disease, ultimately making seminal observations that helped establish the field of HIV immunopathogenesis.

The laboratory has used investigational therapeutic interventions to further the understanding of HIV pathogenesis and pioneered the strategies of immunologically compatible bone marrow transplantation and the adoptive transfer of lymphocytes. The lab has also examined the roles of cytokines in treating patients with HIV infection.

The Immunopathogenesis Section investigates the cellular and molecular mechanisms underlying the immune dysfunction caused by HIV infection. Several major projects ongoing in the section are described below.

Role of HIV envelope-target cell interactions in the pathogenesis of HIV infection (Lead Investigators: James Arthos, Ph.D., and Claudia Cicala, Ph.D.)

The primary aim of this project is to better understand the role of the HIV envelope protein in HIV pathogenesis. To that end, we have focused on the complex interplay between the viral envelope and several of the known cell surface receptors to which it binds (CD4, CCR5, CXCR4, integrin α4β7). Understanding the complexities and significance of the signaling processes that gp120 mediates will enhance our understanding of HIV-1 pathogenesis and may facilitate the discovery of new strategies for the treatment and prevention of HIV-1 disease. The finding that gp120 engages integrin α4β7, the gut-homing receptor, opens up many new and potentially important questions. Because α4β7 mediates leukocyte homing to gut-associated lymphoid tissue (GALT), which is a principal site of HIV replication during the acute phase of infection, we explored the role of α4β7-expressing CD4+ T cells in HIV transmission. We previously determined that human α4β7high CD4+ T cells are highly susceptible in vitro to productive infection by HIV, in part because α4β7high CD4+ T cells are enriched with metabolically active cells. We then tested this hypothesis in a non-human primate in vivo model of HIV/SIV infection and determined that an antibody specific for α4β7 prevented transmission in a rhesus macaque model of mucosal transmission. In addition, we have investigated the interaction between HIV and α4β7 on primary B cells. We have learned that some of the defects associated with HIV disease result from direct interactions between gp120 and receptors on B cells. These findings have relevance to our understanding of early HIV transmission and viral dissemination, particularly in GALT, providing new avenues of investigation regarding the potential role of α4β7+ as a therapeutic target against HIV infection.

Major Findings

• HIV-1 envelope binds to, and signals through α4β7 integrin, the gut mucosal homing receptor for peripheral T cells.
• The HIV envelope protein gp120 binds to a conformationally active form of α4β7 on CD4+ T cells. This binding is independent of the binding of envelope to the CD4 molecule. Because the function of α4β7 is intimately linked to GALT, where HIV replicates at high levels especially in acute/early infection, the specific affinity observed suggests that envelope-α α4β7 interactions play an important role in HIV pathogenesis.
• α4β7high CD4+ T cells are more susceptible to productive infection by HIV than are α4β7low/neg CD4+ T cells, in part because this cellular subset is enriched with metabolically active cells.
• Removal of N-linked glycosylation sites in HIV envelopes results in large increases in the specific affinity of gp120 for α4β7. Several envelopes derived from viruses isolated shortly after transmission react with α4β7 to a substantially higher level than do the great majority of envelopes derived from viruses isolated in the chronic phase of infection. These results suggest that mucosal transmission may frequently involve a relative requirement for the productive infection of α4β7+ CD4+ T cells.
• Targeting α4β7 significantly reduces intravaginal mucosal transmission and subsequent tissue dissemination of SIV in a non-human primate model of HIV/AIDS. This supports our hypothesis that α4β7+/CD4+ T cells can play an important role in mucosal transmission of HIV.