Reservoir cells no longer detectable after a heterologous SHIV challenge with the synthetic HIV-1 Tat Oyi vaccine

Abstract

Background: Extra-cellular roles of Tat might be the main cause of maintenance of HIV-1 infected CD4 T cells or reservoir cells. We developed a synthetic vaccine based on a Tat variant of 101 residues called Tat Oyi, which was identified in HIV infected patients in Africa who did not progress to AIDS. We compared, using rabbits, different adjuvants authorized for human use to test on ELISA the recognition of Tat variants from the five main HIV-1 subtypes. A formulation was tested on macaques followed by a SHIV challenge with a European strain.

Results: Tat Oyi with Montanide or Calcium Phosphate gave rabbit sera able to recognize all Tat variants. Five on seven Tat Oyi vaccinated macaques showed a better control of viremia compared to control macaques and an increase of CD8 T cells was observed only on Tat Oyi vaccinated macaques. Reservoir cells were not detectable at 56 days post-challenge in all Tat Oyi vaccinated macaques but not in the controls.

Conclusion: The Tat Oyi vaccine should be efficient worldwide. No toxicity was observed on rabbits and macaques. We show in vivo that antibodies against Tat could restore the cellular immunity and make it possible the elimination of reservoir cells.

Figure 1

Viral load of rhesus macaques vaccinated with Tat Oyi (panel A) and control macaques vaccinated with β-gal (panel B) following SHIV challenge (SHIV-BX08). The 965 (white square), 966 (no symbol), 969 (black circle), 975 (black square), 9611 (white circle), 9711 (white triangle) and 9712 (black triangle) macaques are the Tat Oyi vaccinated macaques. The 963 (white square), 964 (black square), 978 (white circle) and 9610 (black circle) Macaques are the controls vaccinated with β-gal. Two vaccinated macaques (965 and 969) on five had a viremia up to or superior to 1 millions RNA copies/ml that similar to controls. Macaque 966 had a viremia almost undetectable after the first SHIV challenge and remained at the same level in spite of a second challenge with SHIV 162P 3.2 seven weeks after the first challenge. The other macaques were not challenged twice. Control macaque 963 had an unexpected low viremia. Panel C: Grey bars indicate the post infection viremia in the plasma at two weeks and the black bars indicate viremia at nine weeks post-infection of the challenged macaques. Macaque 966 has a higher viremia at nine weeks due to its second SHIV challenge.

Figure 2

HIV infected CD4 T cell (reservoir cells) in rhesus macaques vaccinated with Tat Oyi (panel A) and control macaques vaccinated with β-gal (panel B) following SHIV challenge. The 965 (white square), 966 (no symbol), 969 (black circle), 975 (black square), 9611 (white circle), 9711 (white triangle) and 9712 (black triangle) Macaques are the Tat Oyi vaccinated Macaques. The 963 (white square), 964 (black square), 978 (white circle) and 9610 (black circle) Macaques are the controls vaccinated with β-gal. The upper panel shows that no reservoir cells were detectable in the seven Tat Oyi vaccinated macaques after 56 days although macaques 965 and 969 had high viremia peaks (Fig 1). Interestingly, no reservoir cells were detectable at any time for macaque 966 even after its second SHIV challenge.

Figure 3

CD8+ cell count of challenged Macaques. The 963, 964, 978 and 9610 Macaques are the controls. The 965, 966, 969, 975, 9611, 9711 and 9712 Macaques are the vaccinated Macaques. Striped histograms represent the CD8+ cell count at the day of challenge. Black histograms represent the CD8+ cell count 9 weeks post-challenge whilst grey histograms represent the CD8+ cell count 18 weeks post-challenge.

Figure 4

Antibody response against Tat for the seven macaques vaccinated with Tat Oyi. The 965 (white square), 966 (no symbol), 969 (black circle), 975 (black square), 9611 (white circle), 9711 (white triangle) and 9712 (black triangle) Macaques are the Tat Oyi vaccinated Macaques. Macaque 966 in the top had the best response against Tat and turned to have the best control of the viremia with no reservoir cells detected (Fig 1 & 2). The left axis shows the OD of 1/100 sera dilution.

Figure 5

Antibodies titers against GP120. The 965 (white square), 966 (no symbol), 969 (black circle), 975 (black square), 9611 (white circle), 9711 (white triangle) and 9712 (black triangle) Macaques are the Tat Oyi vaccinated Macaques. The 963 (white square), 964 (black square), 978 (white circle) and 9610 (black circle) Macaques are the controls vaccinated with β-gal. Six from the seven macaques vaccinated with Tat Oyi had a high level of GP120 antibodies (panel A) similar to the macaques controls (panel B). Antibodies against GP120 appears to not have play a role in the elimination of reservoir cells. This is well illustrated with macaque 966 (Panel A) that had no antibody against GP120 after the first challenge SHIV and a low level of antibodies after its second SHIV challenge.