AIDS and tuberculosis annually kill more than three million people worldwide and the numbers are growing. Of the >40 million adults and 5 million children infected with HIV, 95 percent live in developing countries and about one-third are co-infected with M. Tb. As many as half of HIV-infected patients in Africa have M. Tb and up to 80 percent of M. Tb-infected patients are infected with HIV. People co-infected with both HIV and M. Tb have a 100-fold greater risk of developing active M. Tb disease and becoming infectious, increasing the spread of disease even further and faster. If active M. Tb goes untreated in HIV+ patients, most will die within one year.
M. Tb is the most common opportunistic infection occurring in HIV-infected individuals in resource poor countries and it accelerates HIV-associated morbidity and mortality as well as viral replication . Studies have shown increased transcription of the HIV long terminal repeat (LTR) in cultured monocytic cells exposed to either live M. Tb or cell wall components . In these same studies anti-TNF antibodies reduced the increased transcription of the HIV LTR by >50% . Kitaura et al.  demonstrated that incubation of U1, a chronically HIV-infected human promonocytic cell line, with various strains of mycobacteria resulted in enhanced p24 antigen release into the supernatant. The amount of TNF produced by U1 cells correlated with p24 antigen release and antibody to TNF inhibited p24 release induced by mycobacteria. In a recent review Collins et al.  postulate that higher viral loads, increased HIV diversity, and changes in cytokine/chemokine levels in HIV-infected individuals with M. Tb appear to be related to a localized immune stimulation. They suggest that increased levels of TNF and MCP-1, induced by M. Tb, may activate HIV replication in lymphocytes, monocytes, and macrophages that are resident or have migrated to M. Tb-infected organs, such as the pleura or lung. In addition, studies from the same group demonstrated that the HIV present in blood, following a M. Tb-mediated burst in load and diversity, is phylogenetically related to HIV clones that have evolved independently in M. Tb-infected lung or pleural compartments . The potential of MCP-1 (CCL2) to upregulate HIV replication was also confirmed by Fantuzzi et al.  who reported that infection of monocyte-derived macrophages with laboratory-adapted HIV or primary viral isolates in the continuous presence of anti-CCL2 antibody resulted in significantly lower p24 release compared to control cultures. Further, CCL2 neutralization resulted in the intracellular accumulation of p24 antigen and they suggested that CCL2 might represent an autocrine factor important for enhancing virion production, most likely by affecting the macrophage cytoskeleton.
Other organisms also enhance HIV replication through increased TNF production. Zhao et al.  reported that the protozoan parasite Leishmania enhances both HIV virus transcription and production in human tonsillar tissue infected ex vivo. Use of pentoxifylline and neutralizing anti-TNF or anti-IL-1-alpha antibodies showed that this Leishmania-mediated increase in HIV production was linked to increased production of TNF and IL-1-alpha.
As noted above, TNF-mediated enhancement also applies to the replication of M. Tb. Engele et al.  demonstrated that infection of human alveolar macrophage (AM) with virulent strains of mycobacteria induced the secretion of significantly higher levels of TNF than attenuated strains and that TNF levels correlated with the ability of the mycobacteria to multiply intracellularly. Treatment of infected macrophages with anti-TNF antibodies reduced, while exogenously-added TNF enhanced, the growth rate of intracellular bacteria.
Studies supporting the potential role of TNF in HIV replication and pathogenesis are those of De et al. , who used HIV-transgenic mice (tg26) which appear normal at birth but die within 3- 4 weeks. The skin of these transgenic mice shows diffuse scaling and expresses high levels of both HIV mRNA and gp120. Sera of Tg26 mice have a 50-fold increase in TNF levels compared to those of non-transgenic mice. Treatment with antibody to TNF reduced serum TNF levels by ~75%, prevented death, resulted in near normal growth, and produced a marked decrease in skin lesions and a profound reduction in the expression of HIV mRNA and gp120. Sha et al.  reported the results of a clinical study in which etanercept (Enbrel®; dimerized soluble TNF receptor) was used for as a single bolus to treat HIV-infected subjects who had already received 12 weeks of HAART (highly active antiretroviral therapy) followed by an additional 16 weeks of HAART with or without recombinant human interleukin-2 (rhIL-2). Plasma IL-6 and C-reactive protein levels increased after rhIL-2 treatment but etanercept pretreatment blunted these increases and appeared to be well tolerated. Recently, Wallis et al.  reported on a 28-day Phase I safety study of etanercept in 16 patients co-infected with HIV-1 and M. Tb. Etanercept (25 mg) was administered twice weekly, beginning on day 4 of the M. Tb therapy, for 4 weeks. Controls were 42 CD4-frequency-matched patients with sputum smear-positive M. Tb and CD4 cell counts >200 cells/μl. In etanercept-treated subjects trends toward superior responses to M. Tb treatment were evident in body mass, performance score, number of involved lung zones, cavitary closure, and time to sputum culture conversion. Etanercept treatment resulted in a 25% increase in CD4 cells by week 4 although none of these positive trends were statistically significant because of the low number of patients enrolled in this Phase I study.
Thus, several studies suggest that minimizing TNF levels in both HIV and M. Tb-infected patients might decrease both the replication of each pathogen as well as the pathogenesis associated with co-infection of these two agents. Furthermore, pilot clinical studies suggest that TNF levels can be safely lowered in conjunction with existing antiretroviral or anti-M. Tb therapies. Currently-marketed TNF antagonists are proteins requiring injection and with relatively long half-lives, making it more difficult to cease TNF antagonism once it has been initiated. In the present study we sought to determine whether LMP-420, an anti-inflammatory nucleoside analog that is a potent inhibitor of TNF and MCP-1 synthesis, would block the replication of either HIV or virulent M. Tb in human primary cell cultures and whether LMP-420 might synergize with AZT to inhibit HIV replication.