Gene editing of donor stem cells prior to transplantation into a patient with both HIV infection and acute lymphoblastic leukemia (ALL) was safe and effectively treated the patient’s leukemia, but failed to resolve his HIV, investigators reported.
The 27-year-old man received an HLA-matched transplant of hematopoietic stem and progenitor cells (HSPCs) that had been genetically engineered to lack CCR5, a key gateway for HIV entry into cells.
Although the transplant resulted in complete remission of leukemia with full donor chimerism, only about 9% of the posttransplant lymphocytes showed disruption of CCR5, and during a brief trial of antiretroviral therapy interruption his HIV viral load rebounded, reported Hongkui Deng, PhD, and colleagues from Peking University in China.
Although the experiment did not meet its goal of a drug-free HIV remission, it serves as a proof of concept for the use of CRISPR-Cas9 (clustered regularly interspaced palindromic repeats/CRISPR-associated protein 9) gene editing to treat HIV infection, the authors contend.
“These results show the proof of principle that transplantation and long-term engraftment of CRISPR-edited allogeneic HSPCs can be achieved; however, the efficiency of the response was not adequate to achieve the target of cure of HIV-1 infection,” they wrote in a brief report published in the.
As, other research groups have investigated genetic editing to mimic a naturally occurring mutation that effectively disables the CCR5 HIV coreceptor, preventing the retrovirus from entering healthy cells. The mutation was first identified in a man named Timothy Brown who came to be known as “the Berlin patient” after he was apparently cured of HIV infection after a bone marrow transplant from a donor who had the mutation.
Dr. Deng and colleagues took advantage of HSPC transplantation, a standard therapy for ALL to see whether it could also have beneficial effects on concomitant HIV infection.
They treated donor HSPCs with CRISPR-Cas9 to ablate CCR5 and then delivered them to the patient along with additional CD34-depleted donor cells from mobilized peripheral blood.
The transplant was a success, with neutrophil engraftment on day 13 and platelet engraftment on day 27, and the leukemia was in morphologic complete remission at week 4 following transplantation. The patient remained in complete remission from leukemia throughout the 19-month follow-up period, with full donor chimerism .
However, when a planned interruption of antiretroviral therapy was carried out at 7 months post transplant, the serum viral load increased to 3 × 107 copies/ml at week 4 following interruption, and the patient was restarted on the drug. His viral levels gradually decreased to undetectable level during the subsequent months.
The investigators noted that 2 weeks after the drug interruption trial was started there was a small increase in the percentage of CCR5 insertion/deletions.
“The low efficiency of gene editing in the patient may be due to the competitive engraftment of the coinfused HSPCs in CD34-depleted cells and the persistence of donor T cells. To further clarify the anti-HIV effect of CCR5-ablated HSPCs, it will be essential to increase the gene-editing efficiency of our CRISPR-Cas9 system and improve the transplantation protocol,” they wrote.
The study was funded by the Beijing Municipal Science and Technology Commission and others (unspecified). All authors reported having nothing to disclose.