Cure of HIV infection was observed following stem cell transplantation (SCT) with homozygous CCR5Δ32 donor cells in the Berlin patient. In contrast, in the Boston patients, transplanted with a regular donor, HIV rebound was observed after treatment interruption despite loss of detectable HIV DNA in PBMCs. It is unclear which reservoir fueled HIV rebound.
The impact of SCT on HIV-1 reservoir size in IciStem patients 5 and 11 was investigated. SCT was performed using HLA-matched CCR5Δ32 donors. Before SCT we performed: 1) Phenotypic and genotypic co-receptor tropism analysis 2) Quantification of the HIV reservoir in CD4 T-cell subsets subsets (Tn, Tcm, Ttm, Tem, and Tscm) and bone marrow using ddPCR 3) Single copy assay (SCA) on plasma. After graft failure, patient 11 was re-transplanted with CCR5Δ32 heterozygous donor cells. Post-SCT viral dynamics and the post-mortem viral reservoir were analyzed using ddPCR.
Patients 5 and 11 harboured CCR5-tropic virus (FPR 89% and 33-49%), were treated with ART since 1999 and 1996, and were effectively suppressed for 5 and 16 years prior to SCT, respectively. Before SCT, no viral RNA was detected in routine diagnostics while SCA in plasma detected 15 c/ml (patient 5) and 2 c/ml (patient 11). In patient 5, HIV DNA was detected in PBMCs (983 c/10^6), naive T-cells (635 c/10^6) and memory T-cells (Tcm, Tm and Tem, 1537, 2832 and 3462 c/10^6). In patient 11, HIV DNA was detected in PBMCs (295 c/10^6), bone marrow (80 c/10^6), stem cell-like CD4 T-cells (490 c/10^6), naive T-cells (579 c/10^6) and memory T-cells (Tcm, Ttm and Tem, 2237, 2854, and 4687 c/10^6). SCT led to full chimerism in the PBMCs of both patients and diminished HIV DNA to undetectable levels (<1 c/10^6). Following the death of patients 5 and 11, 10-15 weeks after SCT, post-mortem analysis revealed that HIV DNA could be detected in ileum (274 and 22 c/10^6), liver (27 and 10 c/10^6), spleen (22 and 30 c/10^6) and lung (31 and 8 c/10^6), and additionally in patient 11 in bone marrow (19 c/10^6) and in CD4 cells from lymph node (40 c/10^6).
Within IciStem, we show that after long-term effective ART HIV DNA can readily be detected in various T-cell subsets. In the neutropenic phase post-SCT, HIV DNA could no longer be detected in PBMCs. In contrast, early after SCT, HIV DNA was still found in ileum, liver, spleen, lung, bone marrow and lymph node, indicating that tissue reservoirs may play an important role as long-standing viral reservoirs.