Induction of long-term protective effects against heterologous challenge in SIVhu-infected macaques

A group of three rhesus macaques were inoculated with SIV isolated from a human (SIVhu) accidentally exposed and infected with SIVsm. Extensive sequence analyses of SIVhu obtained from the human and macaques following infection indicated the presence of truncated nef. Not only did nef fail to repair itself in vivo postinfection (p.i.), but instead, further mutations added additional stop codons with increasing time p.i. Infection of these animals was associated with minimal acute viral replication, followed by undetectable plasma viral loads and only intermittent PCR detection up to 5 years p.i. The three SIVhu infected and three control monkeys were then challenged with the heterologous highly pathogenic SHIV89.6p. All three controls became infected and showed rapid declines in peripheral CD4(+) lymphocytes, disease, and death at 10 and 32 weeks p.i., respectively. In contrast, all three animals previously infected with SIVhu are healthy and exhibit stable CD4(+) lymphocyte levels and undetectable plasma viral loads at >20 months post-SHIV89. 6p challenge. Only transient, low levels of SHIV replication were noted in these animals. Whereas responses to SIVgag/pol were noted, no evidence for SIV/SHIV envelope cross-reactivity was detected by antibody or CTL analyses, suggesting that the protective immune mechanisms to the heterologous challenge isolate were most likely not directed to envelope but rather to other viral determinants.

Simian immunodeficiency viruses of diverse origin can use CXCR4 as a coreceptor for entry into human cells

Primary simian immunodeficiency virus (SIV) isolated from sooty mangabey (SIVsm [n = 6]), stumptail (SIVstm [n = 1]), mandrill (SIVmnd [n = 1]), and African green (SIVagm [n = 1]) primates were examined for their ability to infect human cells and for their coreceptor requirements. All isolates infected human peripheral blood mononuclear cells (PBMCs) from a CCR5(+/+) donor, and seven of eight isolates tested also infected CCR5(-/-) PBMCs. Analysis of coreceptor utilization using GHOST and U87 cell lines revealed that all of the isolates tested used CCR5 and the orphan receptors STRL33 and GPR15. Coreceptors such as CCR2b, CCR3, CCR8, and CX3CR1 were also utilized by some primary SIV isolates. More importantly, we found that CXCR4 was used as a coreceptor by the SIVstm, the SIVagm, and four of the SIVsm isolates in GHOST and U87 cells. These data suggest that primary SIV isolates from diverse primate species can utilize CXCR4 for viral entry, similar to what has been described for human immunodeficiency viruses.

Treatment of thrombocytopenia in chimpanzees infected with human immunodeficiency virus by pegylated recombinant human megakaryocyte growth and development factor

Three chimpanzees experimentally infected with human immunodeficiency virus (HIV) developed significant chronic thrombocytopenia after 5, 4, and 2 years, with peripheral platelet counts averaging 64 +/- 19 x 10(3)/microL (P = .004 compared with 228 +/- 92 x 10(3)/microL in 44 normal control animals), mean platelet volumes of 11.2 +/- 1.8 fL (P > .5 compared with 10.9 +/- 0. 7 fL in normal controls), endogenous thrombopoietin (TPO) levels of 926 +/- 364 pg/mL (P < .001 compared with 324 +/- 256 pg/mL in normal controls), uniformly elevated platelet anti-glycoprotein (GP) IIIa49-66 antibodies, and corresponding viral loads of 534, 260, and 15 x 10(3) RNA viral copies/mL. Pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) was administered subcutaneously (25 microg/kg twice weekly for 3 doses) to determine the effects of stimulating platelet production on peripheral platelet concentrations in this cohort of thrombocytopenic HIV-infected chimpanzees. PEG-rHuMGDF therapy increased (1) peripheral platelet counts 10-fold (from 64 +/- 19 to 599 +/- 260 x 10(3) platelets/microL; P = .02); (2) marrow megakaryocyte numbers 30-fold (from 11.7 +/- 6.5 x 10(6)/kg to 353 +/- 255 x 10(6)/kg; P = .04); (3) marrow megakaryocyte progenitor cells fourfold (from a mean of 3.6 +/- 0.6 to 14.1 x 10(3) CFU-Meg/1, 000 CD34(+) marrow cells); and (4) serum levels of Mpl ligand from 926 +/- 364 pg/mL (endogenous TPO) to predosing trough levels of 1, 840 +/- 353 pg/mL PEG-rHuMGDF (P = .02). The peripheral neutrophil counts were also transiently increased from 5.2 +/- 2.6 x 10(3)/microL to 9.9 +/- 5.0 x 10(3)/microL (P = .01), but neither the erythrocyte counts nor the reticulocyte counts were altered significantly (P > .1). The serum levels of antiplatelet GPIIIa49-66 antibodies exhibited reciprocal reductions during periods of thrombocytosis (P < .07). PEG-rHuMGDF therapy did not increase viral loads significantly (395, 189, and 53 x 10(3) RNA viral copies/mL; P > .5 compared with baseline values). The striking increase in peripheral platelet counts produced by PEG-rHuMGDF therapy implies that thrombocytopenia in HIV-infected chimpanzees is attributable to insufficient compensatory expansion in platelet production resulting from HIV-impaired delivery of platelets despite stimulated megakaryocytopoiesis. These data suggest that PEG-rHuMGDF therapy may similarly correct peripheral platelet counts in thrombocytopenic HIV-infected patients.

Hematologic and virologic effects of lineage-specific and non-lineage-specific recombinant human and rhesus cytokines in a cohort of SIVmac239-infected macaques

The hematologic abnormalities of SIV and HIV are well described, although the mechanisms that lead to hematopoietic dysfunction are yet to be fully defined. A number of growth factors and cytokines have been used to induce the differentiation, maturation, and proliferation of appropriate lineages, with the aim that such therapy will lead to functional hematopoietic reconstitution. Within this context, some cytokines have been shown to influence HIV and SIV replication in vitro and, in selected cases, in vivo. However, few studies detail the effects of hematopoietic cytokines such as IL-3, Flt-3 ligand, G-CSF, Tpo, and Epo or correlate the effects on virus replication. In an effort to address this issue, we infected 12 rhesus macaques with 500 TCID50 of SIVmac239 and intensively evaluated hematologic, virologic, and immunologic parameters during administration of cytokines. When all animals had lymphadenopathy, hepatosplenomegaly, and CD4+ cell counts > or =1000/microl, subgroups of three rhesus macaques were administered either rhFlt-3; rrIL-3a; combination of rhG-CSF, rhTpo, and rhEpo (rhGET); or rrIL-12. Fourteen days of rhFlt-3 administration induced expansion of the bone marrow CD34+ cells and granulocyte-macrophage colony-forming units (GM-CFUs) and increased absolute peripheral blood CD34+ cells and total CFUs. Following rrIL-3 and rhGET administration absolute peripheral blood CD34+ cells and total CFUs increased. rhGET also increased granulocyte, platelet, and reticulocyte counts by day 14 of administration. Branched DNA and coculture assays did not demonstrate any significant change in viral load with any of the cytokines administered. These data suggest that SIV-infected rhesus macaques have the hematopoietic capability to expand and mobilize CD34+ and GM-CFU progenitors and formed elements at 6-8 months postinfection in response to various cytokines, without increasing viral load.

Simian immunodeficiency viruses containing mutations in the long terminal repeat NF-kappa B or Sp1 binding sites replicate efficiently in T cells and PHA-stimulated PBMCs

The long terminal repeats (LTRs) of primate lentiviruses contain conserved binding sites for the NF-kappa B and Sp1 cellular transcription factors. In order to study the role that these sites play in simian immunodeficiency virus (SIV) replication, we have introduced mutations that disrupt either the NF-kappa B or Sp1 binding sites in the LTR of an infectious molecular clone of SIVmac239. An additional mutation also disrupted the SF3 transcription factor binding site that overlaps the NF-kappa B site. Viruses containing point mutations or deletions of the NF-kappa B, SF3, or Sp1 binding sites retained the ability to replicate efficiently in the CEMx174 and MT4 cell lines, as well as in PHA-stimulated primary rhesus macaque peripheral blood mononuclear cells (PBMCs). Efficient replication of SIVs mutated in either NF-kappa B or Sp1 binding sites suggests that the SIV LTR promoter contains multiple functionally redundant elements capable of supporting sufficient transcription to allow productive viral replication.