Patient and Caregiver Attitudes Towards Gene Therapy for Sickle Cell Disease: A Need for Partnership and Education

Background: Fewer than 20% of patients with sickle cell disease (SCD) have access to curative matched sibling donor bone marrow transplantation (MSD-BMT). Development of novel therapies to ameliorate the serious morbidity and early mortality caused by SCD is a National Institute of Health research priority. Gene therapy for SCD has emerged as a promising approach in early-stage clinical trials approach with the potential to reach greater numbers of patients than MSD-BMT. Knowledge and attitudes of individuals with SCD towards this investigational new therapy and their willingness to participate in early-stage clinical trials have not been systematically described. Methods: Patients with SCD at least 13 years of age (n=66) and caregivers of children with SCD (n=38) were surveyed about knowledge, attitudes, and beliefs regarding gene therapy for SCD. Most questions utilized a 5-item Likert response scale while The Newest Vital Sign was used to assess health literacy. To explore attitudes around gene therapy in further detail, we identified a regionally diverse focus group comprised of 12 patients/caregivers with SCD from across the United States. We audio-recorded, transcribed verbatim, and analyzed five focus group discussions using thematic content analysis to identify salient themes related to attitudes towards gene therapy for SCD. Our goal was to identify the educational needs and preferences of this patient / caregiver stakeholder group. Results: Survey: Of the 104 survey respondents 96% identified as Black and 4% as Hispanic. Respondents were between 13-64 years (mean 29.6, Std Dev 11.9 years). HbSS and HbSC were the most common genotypes (61.5% and 24%, respectively). Only 4.8% of participants (N=5) felt "extremely knowledgeable" about gene therapy for SCD while most (63.4%) reported no/slight knowledge. We found no association between health literacy levels and gene therapy knowledge (p=0.361). Nearly 30% of participants reported that the risk of cancer as a potential side effect would "probably not prevent their enrollment" on a gene therapy trial while 48% said it "definitely/probably would preclude their participation". Most respondents had a neutral attitude regarding the safety of gene therapy for SCD and how good of a treatment it was (56.7% and 58.6%, respectively). Only a few respondents endorsed the idea that gene therapy was "unsafe" or "not a good treatment for SCD" (5.8% and 4.8% respectively). There was an association between increasing knowledge about gene therapy and agreement that it is safe (p=0.012) and a good treatment for SCD (p=0.031). Focus Groups: Among the focus group participants, there was consensus that communication about gene therapy is suboptimal. Participants noted that clinicians frequently use medical jargon, do not tailor their approach to the individual patient/caregiver, and fail to adequately disclose important details. Focus group members desired more information about side effects and risks associated with conditioning chemotherapy, immunosuppression, risk of infertility, and hair loss. Participants, particularly parents of children with SCD, were worried about future unknown risks and described the enormity of the decision to enroll in an early-phase trial. Focus group members verbalized the need for inclusion of patients with SCD as partners during the informed consent/assent process and ideally, at the outset of the clinical trial design. Conclusion: Very few patients with SCD described feeling knowledgeable about gene therapy for SCD; a majority have neutral feelings about the safety and utility ("good treatment for SCD") of this new approach. Patient/caregiver-centered education about gene therapy in a manner that meets stakeholder informational needs is urgently needed. Given the temporary hold on lentiviral gene therapy trials for SCD (after some participants developed a myeloid neoplasm on an industry sponsored trial in February 2021) and the risk of cancer as a probable or definite barrier to enrollment in a gene therapy trial for many patients, transparency of information about these risks is essential. For the successful execution of novel trials in SCD, a community-based participatory research approach is vital. Disclosures Sharma: Medexus Inc: Consultancy; Spotlight Therapeutics: Consultancy; Novartis: Other: Salary support paid to institution; Vertex Pharmaceuticals/CRISPR Therapeutics: Other: Salary support paid to institution; Vindico Medical Education: Honoraria; CRISPR Therapeutics: Other, Research Funding. Johnson: CRISPR Therapeutics: Research Funding.

Leukemia after gene therapy for sickle cell disease: insertional mutagenesis, busulfan, both or neither

Recently, encouraging data provided long-awaited hope for gene therapy as a cure for sickle cell disease (SCD). Nevertheless, the suspension of the bluebird bio gene therapy trial (ClinicalTrials.gov: NCT02140554) after participants developed acute myeloid leukemia/myelodysplastic syndrome (AML/MDS) is concerning. Potential possibilities for these cases include busulfan, insertional mutagenesis, both or neither. Busulfan was considered the cause in the first reported case, as the transgene was not present in the AML/MDS. However, busulfan is unlikely to have contributed to the most recent case. The transgene was present in the patient's malignant cells, indicating they were infused after busulfan treatment. Several lines of evidence suggest an alternative explanation for events in the bluebird bio trial, including that SCD population studies show an increased relative, but a low absolute, risk of AML/MDS. We propose a new hypothesis: after gene therapy for SCD, the stress of switching from homeostatic to regenerative hematopoiesis by transplanted cells drives clonal expansion and leukemogenic transformation of pre-existing premalignant clones, eventually resulting in AML/MDS. Evidence validating our hypothesis will support pre-screening individuals with SCD for pre-leukemic progenitors before gene therapy. Until a viable, safe strategy has been implemented to resume gene therapy in adults with severe SCD, reasonable alternative curative therapy should be considered for children and adults with severe SCD. Currently, open multi-center clinical trials are incorporating nonmyeloablative conditioning, related haploidentical donors, and post-transplantation cyclophosphamide. Preliminary results from these trials appear promising and NIH-sponsored trials are ongoing in pediatric and adult individuals with SCD using this platform.

Emerging Immunogenicity and Genotoxicity Considerations of Adeno-Associated Virus Vector Gene Therapy for Hemophilia

Adeno-associated viral (AAV) vector gene therapy has shown promise as a possible cure for hemophilia. However, immune responses directed against AAV vectors remain a hurdle to the broader use of this gene transfer platform. Both innate and adaptive immune responses can affect the safety and efficacy of AAV vector–mediated gene transfer in humans. These immune responses may be triggered by the viral capsid, the vector’s nucleic acid payload, or other vector contaminants or excipients, or by the transgene product encoded by the vector itself. Various preclinical and clinical strategies have been explored to overcome the issues of AAV vector immunogenicity and transgene-related immune responses. Although results of these strategies are encouraging, more efficient approaches are needed to deliver safe, predictable, and durable outcomes for people with hemophilia. In addition to durability, long-term follow-up of gene therapy trial participants will allow us to address potential safety concerns related to vector integration. Herein, we describe the challenges with current methodologies to deliver optimal outcomes for people with hemophilia who choose to undergo AAV vector gene therapy and the potential opportunities to improve on the results.