Defective HIV-1 provirus found in peripheral T lymphocytes and granulocytes in an AIDS patient imply viral infection of progenitor cells

Hematopoietic stem/precursor cells as HIV reservoirs

PURPOSE OF REVIEW

Although latent HIV-1 infection in CD4+ T cells contributes to HIV persistence, there is mounting evidence that other viral reservoirs exist. Here, we review recent data suggesting that the infection of hematopoietic progenitor cells creates additional reservoirs for HIV in vivo.

RECENT FINDINGS

New studies suggest that some types of hematopoietic progenitor cells have the potential to generate reservoirs for HIV. This review focuses on two types that can be infected by HIV in vitro and in vivo: multipotent hematopoietic progenitor cells in the bone marrow and circulating mast cell progenitors. Of these two types, only CD34+ bone marrow cells have been shown to harbor latent provirus in HIV-positive individuals with undetectable viral loads on highly active antiretroviral therapy (HAART). Latent infection of these long-lived cell types may create a significant barrier to HIV eradication; the infection of hematopoietic stem cells in particular could lead to an HIV reservoir that does not appreciably decay over the lifespan of the host.

SUMMARY

To eradicate HIV infection, it will be necessary to purge all viral reservoirs in the host. The findings highlighted here suggest that multipotent hematopoietic progenitor cells and possibly tissue mast cells may constitute significant reservoirs for HIV that must be addressed in order to eliminate HIV infection. Future studies are needed to determine which types of CD34+ cells are infected in vivo and whether infected CD34+ cells contribute to residual viremia in people with undetectable viral loads on HAART.

HIV-1 infection of bone marrow hematopoietic progenitor cells and their role in trafficking and viral dissemination

Patients with HIV-1 often present with a wide range of hematopoietic abnormalities, some of which may be due to the presence of opportunistic infections and to therapeutic drug treatments. However, many of these abnormalities are directly related to HIV-1 replication in the bone marrow (BM). Although the most primitive hematopoietic progenitor cells (HPCs) are resistant to HIV-1 infection, once these cells begin to differentiate and become committed HPCs they become increasingly susceptible to HIV-1 infection and permissive to viral gene expression and infectious virus production. Trafficking of BM-derived HIV-1-infected monocytes has been shown to be involved in the dissemination of HIV-1 into the central nervous system (CNS), and it is possible that HIV-1 replication in the BM and infection of BM HPCs may be involved in the early steps leading to the development of HIV-1-associated dementia (HAD) as an end result of this cellular trafficking process. In addition, the growth and development of HPCs in the BM of patients with HIV-1 has also been shown to be impaired due to the presence of HIV-1 proteins and changes in the cytokine milieu, potentially leading to an altered maturation process and to increased cell death within one or more BM cell lineages. Changes in the growth and differentiation process of HPCs may be involved in the generation of monocyte populations that are more susceptible and/or permissive to HIV-1, and have potentially altered trafficking profiles to several organs, including the CNS. A monocyte subpopulation with these features has been shown to expand during the course of HIV-1 disease, particularly in HAD patients, and is characterized by low CD14 expression and the presence of cell surface CD16.

Expression of CD4 on human peripheral blood neutrophils

CD4, the primary receptor for entry of HIV, is known to be expressed on T cells and monocytes/macrophages; healthy natural killer (NK) lymphocytes; in vitro human herpesvirus 6 (HHV6)-infected CD8+, NK, and gammadelta T lymphocytes; CD34+ progenitor cells; and a subset of eosinophils and basophils. We here report the unconventional expression of CD4 at the surface of peripheral blood neutrophils derived from 4 of 51 (7.8%) HIV-1-infected and 3 of 25 (12%) uninfected donors, with similar frequency within the 2 groups. The percentage of CD4+ neutrophils ranged from 39% to 97% of the total neutrophil population. Both surface and cytoplasmic forms of CD4 were present in neutrophils. Quantitative RNA polymerase chain reaction (PCR) revealed that neutrophils contain levels of CD4 mRNA comparable to those of peripheral blood mononuclear cells derived from the same donor. The conformation of CD4 expressed at the surface of neutrophils was similar to that of CD4 expressed on T lymphocytes as determined by the binding of monoclonal antibodies specific for conformational epitopes and the binding of recombinant HIV-1 gp120. Thus, our data provide evidence that neutrophils express endogenous CD4 and bind HIV. Owing to their abundance in peripheral blood, CD4+ neutrophils may influence significantly the biodistribution of HIV delivering it to sites of inflammation or to additional tissue reservoirs.

Selection of human immunodeficiency virus type 1 variants with an insertion mutation in the p6(gag) and p6(pol) genes under highly active antiretroviral therapy

We detected several types of human immunodeficiency virus type 1 (HIV-1) variants with an insertion mutation in the p6(gag)and p6(pol) genes in eight of twenty-two (36.4%) patients who possessed drug-resistant viruses under highly active antiretroviral therapy (HAART). It was characteristic that a conserved proline-rich motif "PTAPP" in the N-terminus of p6(gag) protein was completely or partially duplicated in all cases. Five among the eight cases were retrospectively investigated in terms of the occurrence of dynamic change in the gag gene between the inserted and wild-type HIV-1 in the course of HAART. The longitudinal analysis revealed the following: 1) The inserted-type viruses were selected over the wild-type during HAART in three cases in which the both types coexisted in the beginning of the therapy. 2) In two cases in which the inserted-type HIV-1 alone was detected before the beginning of HAART, the inserted-type HIV-1 alone was continuously detected during the therapy. The inserted-type HIV-1 was also detected in four of thirty-nine (10.3%) therapy-naive patients. However, the frequency of inserted-type HIV-1 detection in the HAART-receiving patients is significantly higher than that in the therapy-naive patients (P = 0.02). These results suggest that this type of insertion mutation is a polymorphism of the p6(gag) and p6(pol) genes, however, it consequently gave an advantage on proliferation and/or survival of the HIV-1 variant under the presence of antiretroviral drugs.