HIV-positive injecting drug users who are infected with HTLV-II less are less likely to progress to AIDS

HIV-positive injecting drug users who are also infected with human T-cell lymphotropic virus type II (HTLV-II) are less likely to progress to AIDS than HIV-positive drug users who are only infected with HIV, according to an Italian study published in the January 1^st edition of the Journal of Acquired Immune Deficiency Syndromes. The investigators found that in thirteen years of follow-up, 14% of injecting drug users who were infected with both HIV and HTLV-II did not experience significant HIV disease progression compared to only 1% of drug users who were only HIV- infected.

HTLV-II infects CD4 and CD8 cells. Although HTLV-I has been associated with the development of leukaemia, infection with HTLV-II has not been shown to be associated with any specific syndromes.

Infection with HTLV-II became endemic amongst injecting drug users in Europe in the second half of the 20^th century and there has been some debate as to whether infection with the virus accelerates or slows the course of HIV disease.

Italian investigators screened 3600 injecting drug users for infection with both HIV and HTLV-II from 1986 onwards and compared disease progression between patients who were infected with both HIV and HTLV-II and those who were only infected with HIV for an average of thirteen years.

“Our data point to a protective role of HTLV-II infection by preventing loss of CD4 T cells and delaying AIDS progression in some coinfected individuals”, write the investigators.

A total of 1% of HIV-negative individuals were infected with HTLV-II, but this increased to 7% in HIV-positive individuals.

The investigators compared rates of long-term non-progression of HIV disease in 437 patients who were only infected with HIV and 96 individuals who were coinfected with HIV and HTLV-II. Patients were matched for baseline CD4 cell count and age. Long-term non-progression was defined by the investigators as the maintenance of a CD4 cell count above 500 cells/mm³, a viral load below 1,500 copies/ml and no opportunistic infections without the use of anti-HIV therapy.

In an average of 13 years of follow-up, 14% of coinfected patients remained long-term non-progressors compared to only 1% of individuals who were only infected with HIV. The investigators did, however, observe that injecting drug users with both HIV and HTLV-II were significantly more likely to be infected with hepatitis C virus (44%) than HIV monoinfected patients (11%, p

Analysis was then restricted to five individuals coinfected with HIV and HTLV-II to see what the impact of antiretroviral therapy was on both infections. The investigators found that although these patients had a good response to HIV treatment, experiencing both an increase in their CD4 cell count and a fall in their HIV viral load, their HTLV-II viral load increased approximately three-fold after the completion of the first year of HIV therapy. The investigators suggest that this increase was because of an increase in the individuals’ CD8 cell counts – HTLV-II infects CD8 cells.

No illness associated with HTLV-II was observed during the course of the study.

“The evidence presented in this study points to a protective role of HTLV-II infection against AIDS progression”, conclude the investigators. “Antiretroviral therapy in coinfected patients is successful at controlling HIV-1, the result of which is an expansion of CD4 and CD8 cells, but is ineffective against HTLV-II infection”, they add.