Intrathymic adeno-associated virus gene transfer rapidly restores thymic function and long-term persistence of gene-corrected T cells

T-cell specific in vivo gene delivery with DART-AAVs targeted to CD8

One of the biggest challenges for in vivo gene therapy are vectors mediating highly selective gene transfer into a defined population of therapy-relevant cells. Here we present DARPin-targeted AAVs (DART-AAVs) displaying DARPins specific for human and murine CD8. Insertion of DARPins into the GH2/GH3 loop of the capsid protein 1 (VP1) of AAV2 and AAV6 resulted in high selectivity for CD8-positive T cells with unimpaired gene delivery activity. Remarkably, the capsid core structure was unaltered with protruding DARPins detectable. In complex primary cell mixtures, including donor blood or systemic injections into mice, the CD8-targeted AAVs were by far superior to unmodified AAV2 and AAV6 in terms of selectivity, target cell viability, and gene transfer rates. In vivo, up to 80% of activated CD8+ T cells were hit upon a single vector injection into conditioned humanized or immunocompetent mice. While gene transfer rates decreased significantly under non-activated conditions, genomic modification selectively in CD8+ T cells was still detectable upon Cre delivery into indicator mice. In both mouse models, selectivity for CD8+ T cells was close to absolute with exceptional detargeting from liver. The CD8-AAVs described here expand strategies for immunological research and in vivo gene therapy options.

Adeno-Associated Virus Vectors-a Target of Cellular and Humoral Immunity-are Expanding Their Reach Toward Hematopoietic Stem Cell Modification and Immunotherapies

All current market-approved gene therapy medical products for in vivo gene therapy of monogenic diseases rely on adeno-associated virus (AAV) vectors. Advances in gene editing technologies and vector engineering have expanded the spectrum of target cells and, thus, diseases that can be addressed. Consequently, AAV vectors are now being explored to modify cells of the hematopoietic system, including hematopoietic stem and progenitor cells (HSPCs), to develop novel strategies to treat monogenic diseases, but also to generate cell- and vaccine-based immunotherapies. However, the cell types that represent important new targets for the AAV vector system are centrally involved in immune responses against the vector and its transgene product as discussed briefly in the first part of this review. In the second part, studies exploring AAV vectors for genetic engineering of HSPCs, T and B lymphocytes, and beyond are presented.

Delivering CRISPR to the HIV-1 reservoirs

Human immunodeficiency virus type 1 (HIV-1) infection is well known as one of the most complex and difficult viral infections to cure. The difficulty in developing curative strategies arises in large part from the development of latent viral reservoirs (LVRs) within anatomical and cellular compartments of a host. The clustered regularly interspaced short palindromic repeats/ CRISPR-associated protein 9 (CRISPR/Cas9) system shows remarkable potential for the inactivation and/or elimination of integrated proviral DNA within host cells, however, delivery of the CRISPR/Cas9 system to infected cells is still a challenge. In this review, the main factors impacting delivery, the challenges for delivery to each of the LVRs, and the current successes for delivery to each reservoir will be discussed.

Intrathymic AAV delivery results in therapeutic site-specific integration at TCR loci in mice

Adeno-associated virus (AAV) vectors have been successfully exploited in gene therapy applications for the treatment of several genetic disorders. AAV is considered an episomal vector, but it has been shown to integrate within the host cell genome after the generation of double-strand DNA breaks or nicks. Although AAV integration raises some safety concerns, it can also provide therapeutic benefit; the direct intrathymic injection of an AAV harboring a therapeutic transgene results in integration in T-cell progenitors and long-term T-cell immunity. To assess the mechanisms of AAV integration, we retrieved and analyzed hundreds of AAV integration sites from lymph node-derived mature T cells and compared these with liver and brain tissue from treated mice. Notably, we found that although AAV integrations in the liver and brain were distributed across the entire mouse genome, >90% of the integrations in T cells were clustered within the T-cell receptor α, β, and γ genes. More precisely, the insertion mapped to DNA breaks created by the enzymatic activity of recombination activating genes (RAGs) during variable, diversity, and joining recombination. Our data indicate that RAG activity during T-cell receptor maturation induces a site-specific integration of AAV genomes and opens new therapeutic avenues for achieving long-term AAV-mediated gene transfer in dividing cells.

Pediatric immune deficiencies: current treatment approaches

PURPOSE OF REVIEW

To summarize the currently available definitive therapies for patients with inborn errors of immunity (IEIs) with a strong focus on recent advances in allogeneic hematopoietic cell transplantation (HCT) and gene therapy, including the use of alternative donors, graft manipulation techniques, less toxic approaches for pretransplant conditioning and gene transfer using autologous hematopoietic stem cells.

RECENT FINDINGS

In the absence of a matched sibling or a matched related donor, therapeutic alternatives for patients with IEIs include alternative donor transplantation or autologous gene therapy, which is only available for selected IEIs. In recent years, several groups have published their experience with haploidentical hematopoietic cell transplantation (HHCT) using different T-cell depletion strategies. Overall survival and event free survival results, although variable among centers, are encouraging. Preliminary results from autologous gene therapy trials with safer vectors and low-dose busulfan conditioning have shown reproducible and successful results. Both strategies have become valid therapeutic options for patients with IEIs. A new promising and less toxic conditioning regimen strategy is also discussed.

SUMMARY

Definitive therapies for IEIs with HCT and gene therapy are in stage of evolution, not only to refine their efficacy and safety but also their reach to a larger number of patients.

Inborn errors of immunity: Recent progress

Recent advances in the field of inborn errors of immunity (IEIs) have been wide in scope, including progress in mechanisms of disease, diagnosis, and management. New gene defects affecting the immune response continue to be reported, as many as 26 in the year 2020. It was noted that the presentation of IEIs might not include recurrent infections in 9% of cases, and that current diagnostic methods can identify molecular causes in 92% of patients with severe combined immunodeficiency. Progress in immunopathogenesis explained mechanisms leading to symptoms of autosomal-recessive hyper-IgE syndrome. There was an emphasis on research in primary antibody deficiencies. The benefit of antibiotic prophylaxis to reduce the frequency of infections was demonstrated in these patients. The regimen of rituximab and azathioprine or mycophenolate was proven effective for chronic granulocytic interstitial pneumonia. The efficacy and adverse events of hematopoietic stem cell transplant in different IEI conditions were reported, as well as different strategies to improve outcomes, supporting its use in immunodeficiency and immunodysregulatory syndromes. The recent pandemic of coronavirus disease 2019 affected patients with IEIs, in particular those with deficiency in the interferon-mediated activation of the immune response. Initial data suggest that coronavirus disease 2019 vaccines might elicit anti-coronavirus disease 2019-neutralizing antibody responses in some patients with IEI conditions.

AAV integration in human hepatocytes

Recombinant adeno-associated viral (rAAV) vectors are considered promising tools for gene therapy directed at the liver. Whereas rAAV is thought to be an episomal vector, its single-stranded DNA genome is prone to intra- and inter-molecular recombination leading to rearrangements and integration into the host cell genome. Here, we ascertained the integration frequency of rAAV in human hepatocytes transduced either ex vivo or in vivo and subsequently expanded in a mouse model of xenogeneic liver regeneration. Chromosomal rAAV integration events and vector integrity were determined using the capture-PacBio sequencing approach, a long-read next-generation sequencing method that has not previously been used for this purpose. Chromosomal integrations were found at a surprisingly high frequency of 1%-3% both in vitro and in vivo. Importantly, most of the inserted rAAV sequences were heavily rearranged and were accompanied by deletions of the host genomic sequence at the integration site.

Lymphotoxin: from the physiology to the regeneration of the thymic function

The members of the Tumor Necrosis Factor (TNF) superfamily, the ligand lymphotoxin α1β2 (LTα1β2) and its unique receptor lymphotoxin β receptor (LTβR), play a pivotal role in the establishment and regulation of the immune system by allowing a tight communication between lymphocytes and stromal cells. Recent advances using transgenic mice harboring a specific deletion of the Ltbr gene in distinct stromal cells have revealed important roles for LTβR signaling in the thymic function that ensures the generation of a diverse and self-tolerant T-cell repertoire. In this review, we summarize our current knowledge on this signaling axis in the thymic homing of lymphoid progenitors and peripheral antigen-presenting cells, the trafficking and egress of thymocytes, the differentiation of medullary thymic epithelial cells, and the establishment of central tolerance. We also highlight the importance of LTα1β2/LTβR axis in controlling the recovery of the thymic function after myeloablative conditioning regimen, opening novel perspectives in regenerative medicine.