The Role of CD4+ Natural Killer Cells in AIDS-Associated Malignancies

Helene Barbara Bernstein, UC Los Angeles

Non-Hodgkin's lymphoma (NHL) is the sixth most common cause of cancer-related mortality in the U.S., and HIV-associated NHL is the second most common AIDS-associated malignancy. The development of NHL can be devastating to HIV-infected individuals, and appears to be linked to immune dysfunction. Natural Killer (NK) cells play an important role in anti-tumor immunity against several malignancies including AIDS-associated NHL. Following HIV infection, there is NK cell dysfunction as well as an increased incidence of NHL, suggesting that NK- mediated anti-tumor immunity is critical in preventing NHL in immunocompetent individuals. We have identified NK cells that express CD4 on their surface from human lymphoid tissues. Our laboratory has also developed an in vitro system in which large numbers of CD4+ NK cells can be produced for functional analysis. These cells, representing a highly activated subset of NK cells, are potent producers of cytokines, mediate cytotoxicity against NHL cells, and migrate in response to the chemotactic factor IL-16. CD4 expressing NK cells are susceptible to HIV infection, however, which downregulates CD4 expression and could impact their function. Exploring the link between HIV infection, NK cell function, and AIDS-associated NHL is critical and has a myriad of implications for clinical treatment strategies.

This proposal describes studies aimed at determining the effectiveness of CD4+ NK cells in protecting against NHL and how that activity is affected by HIV infection using both in vitro and in vivo models. We plan to expand our preliminary data showing that CD4+ NK cells effectively kill the NHL cell lines Ramos, Daudi, and 2F7 by testing them against additional AIDS-associated NHL targets. These targets also produce IL-16, a chemoattractant for our CD4+ NK cells; we aim to determine whether CD4 expressing NK cells migrate towards NHL cells. This could establish a mechanism for getting CD4+ NK cells to sites of tumor burden. CD4 expressing NK cells could play a critical role in preventing NHL tumorigenesis by mediating cytotoxicity and by producing cytokines and chemokines with anti-tumor activity.

HIV infection will then be introduced to our in vitro model to determine how function is impacted. Both wild type and reporter viruses will be used to facilitate sorting live, productively infected cells for use in these assays. We will then utilize the well-established hu-PBL-SCID model to assess whether engraftment of CD4+ NK cells will prevent development of Epstein-Barr virus lymphoproliferative disease (EBV-LPD), a condition resembling AIDS-associated NHL. We hypothesize that after intraperitoneal injection of human peripheral blood lymphocytes, the additional injection of CD4+ NK cells will result in a decreased incidence of tumors/reduced tumor size and increased survival rates when compared to CD4- NK cells or no NK cell control groups. Additionally, we will assess the effect of HIV infection on CD4+ NK cell anti-tumor activity in vivo using this model. We anticipate an increased tumor incidence in comparison to uninfected controls and that this will negatively impact survival. These studies will add to our current understanding of tumor immunology and the function of CD4+ NK cells. These cells could function as an immunotherapeutic agent against AIDS-associated NHL, however, the implications of HIV infection of this cell type require further study as proposed in this grant.