CD4-independent infection of human B cells with HIV type 1: Detection of unintegrated viral DNA

Although B lymphocytes are a major constituent of lymphoid organs and acquire a significantly altered phenotype and function in HIV-infected individuals, it remains unclear whether CD4-negative B cells are a susceptible host for viral entry and long-term productive infection. We screened a number of Epstein-Barr virus (EBV)-positive and -negative Burkitt's lymphoma (BL) B cell lines as well as subpopulations of normal B cells that include tonsillar naive and germinal center/memory B cells for the expression of HIV-1 receptors CD4, CXCR4, and CCR5. Cell lines and resting or activated normal B cells lacked CD4 and CCR5 but expressed CXCR4. We demonstrate HIV-1 infection of a CD4-negative, EBV-negative (BL) cell line, CA46, which remained productively infected yet noncytopathic for more than 36 months in culture. HIV-1 (HTLV-III_B) infection of CA46 cells was mediated through CXCR4 in a CD4-independent manner and correlated with up-regulation of the expression of B cell activation markers CD23 and CD95 (Fas receptor). Despite Fas receptor expression, HIV-1-infected CA46 cells remained resistant to Fas-mediated cell death. CA46-derived, CD4-independent viral isolates were proficient in infecting and causing syncytium formation in Molt4 T cells. The HIV-1 genomic organization in persistently infected CA46 clones was found to be predominantly unintegrated linear and circular DNA. Importantly, naive and germinal center/memory B cells could also be infected by HIV-1 in a CD4-independent manner. Although these B cell subpopulations expressed moderate to high levels of CXCR4, they required activation through CD40 and interleukin 4 receptor for infection. These findings point to B cells as an additional HIV-1 target and suggest a structural evolution of the HIV-1 genome responsible for CD4-independent and noncytopathic infections.