One of the challenges in HIV cure research is developing methods for finding extremely low levels of replication-competent virus. For example, there have been three cases where individuals were considered possibly cured of HIV because the virus could not be detected even though ART had been stopped (the Mississippi baby and two Boston patients), but all ultimately experienced viral load rebounds. The research group of Joel Blankson at Johns Hopkins University is working on an approach to this problem involving mice, and recently published preliminary results in the Journal of Infectious Diseases.
The technique is described as a murine viral outgrowth assay (MVOA) and involves the transfer of human CD4 T cells into immune deficient mice (these mice are more commonly reconstituted with human immune cells to create humanized mice for research purposes). The researchers show that transfer of CD4 T cells from HIV-positive individuals on ART or elite controllers led to the outgrowth of replication-competent HIV in the mice; importantly, virus was detected in the case of one elite controller from whom HIV could not be cultured by normal laboratory methods. The results are in accordance with a previous report involving a post-treatment controller from whom HIV could not be detected using laboratory culture methods but was evident when CD4 T cells were transferred into immune deficient mice; this case has not yet been published, but was presented as a poster at the 7th IAS Conference on HIV Pathogenesis, Treatment and Prevention in 2013 by Jan van Lunzen and colleagues.
The MVOA can only give binary results—replication-competent HIV is either detected or not—but nevertheless could offer a useful additional means of analysis when cases similar to the Mississippi baby and the Boston patients occur in the future.
J Infect Dis. 2015 Apr 15. pii: jiv230. [Epub ahead of print]
Metcalf Pate KA, Pohlmeyer CW, Walker-Sperling VE, Foote JB, Najarro KM, Cryer CG, Salgado M, Gama L, Engle EL, Shirk EN, Queen SE, Chioma S, Vermillion MS, Bullock B, Li M, Lyons CE, Adams RJ, Zink MC, Clements JE, Mankowski JL, Blankson JN.
BACKGROUND: Sensitive assays are needed for detection of residual HIV in patients with undetectable plasma viral loads to determine if eradication strategies are effective. The gold standard quantitative viral outgrowth assay (QVOA) underestimates the magnitude of the viral reservoir. We sought to determine whether xenograft of leukocytes from HIV-1 infected patients with undetectable plasma viral loads into immunocompromised mice would result in viral amplification.
METHODS: Peripheral blood mononuclear cells (PBMCs) or purified CD4+ T cells from HIV/SIV infected subjects with undetectable plasma viral loads were adoptively transferred into NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice. The mice were monitored for viremia following depletion of human CD8+ T cells to minimize antiviral activity. In some cases humanized mice were also treated with activating anti-CD3 antibody.
RESULTS: With this murine viral outgrowth assay (MVOA), we successfully amplified replication-competent HIV-1/SIV from all subjects tested including 5 HIV+ patients on suppressive antiretroviral therapy (ART) and 6 elite controllers or suppressors (ES) who maintain undetectable viral loads without ART, including an ES from whom we were unable to recover virus by QVOA.
CONCLUSIONS: Our results suggest that the MVOA has the potential to serve as a powerful tool to identify residual HIV in patients with undetectable viral loads.