Mark B. Geyer

IgH class switching and translocations use a robust non-classical end-joining pathway.

Immunoglobulin variable region exons are assembled in developing B cells by V(D)J recombination. Once mature, these cells undergo class-switch recombination (CSR) when activated by antigen. CSR changes the heavy chain constant region exons (Ch) expressed with a given variable region exon from Cμ to a downstream Ch (for example, Cγ, Cε or Cα), thereby switching expression from IgM to IgG, IgE or IgA. Both V(D)J recombination and CSR involve the introduction of DNA double-strand breaks and their repair by means of end joining. For CSR, double-strand breaks are introduced into switch regions that flank Cμ and a downstream Ch, followed by fusion of the broken switch regions. In mammalian cells, the ‘classical’ non-homologous end joining (C-NHEJ) pathway repairs both general DNA double-strand breaks and programmed double-strand breaks generated by V(D)J recombination. C-NHEJ, as observed during V(D)J recombination, joins ends that lack homology to form ‘direct’ joins, and also joins ends with several base-pair homologies to form microhomology joins. CSR joins also display direct and microhomology joins, and CSR has been suggested to use C-NHEJ. Xrcc4 and DNA ligase IV (Lig4), which cooperatively catalyse the ligation step of C-NHEJ, are the most specific C-NHEJ factors; they are absolutely required for V(D)J recombination and have no known functions other than C-NHEJ. Here we assess whether C-NHEJ is also critical for CSR by assaying CSR in Xrcc4- or Lig4-deficient mouse B cells. C-NHEJ indeed catalyses CSR joins, because C-NHEJ-deficient B cells had decreased CSR and substantial levels of IgH locus (immunoglobulin heavy chain, encoded by Igh) chromosomal breaks. However, an alternative end-joining pathway, which is markedly biased towards microhomology joins, supports CSR at unexpectedly robust levels in C-NHEJ-deficient B cells. In the absence of C-NHEJ, this alternative end-joining pathway also frequently joins Igh locus breaks to other chromosomes to generate translocations.

CD19-targeted CAR T-cell therapeutics for hematologic malignancies: interpreting clinical outcomes to date.

Adoptive transfer of T cells genetically modified to express chimeric antigen receptors (CARs) targeting CD19 has produced impressive results in treating patients with B-cell malignancies. Although these CAR-modified T cells target the same antigen, the designs of CARs vary as well as several key aspects of the clinical trials in which these CARs have been studied. It is unclear whether these differences have any impact on clinical outcome and treatment-related toxicities. Herein, we review clinical results reflecting the investigational use of CD19-targeted CAR T-cell therapeutics in patients with B-cell hematologic malignancies, in light of differences in CAR design and production, and outline the limitations inherent in comparing outcomes between studies.

Rituximab and FAB/LMB 96 chemotherapy in children with Stage III/IV B-cell non-Hodgkin lymphoma: a Children’s Oncology Group report

Rituximab and FAB/LMB 96 chemotherapy in children with Stage III/IV B-cell non-Hodgkin lymphoma: a Children’s Oncology Group report

A comparison of immune reconstitution and graft-versus-host disease following myeloablative conditioning versus reduced toxicity conditioning and umbilical cord blood transplantation in paediatric recipients

Immune reconstitution appears to be delayed following myeloablative conditioning (MAC) and umbilical cord blood transplantation (UCBT) in paediatric recipients. Although reduced toxicity conditioning (RTC) versus MAC prior to allogeneic stem cell transplantation is associated with decreased transplant‐related mortality, the effects of RTC versus MAC prior to UCBT on immune reconstitution and risk of graft‐versus‐host disease (GVHD) are unknown. In 88 consecutive paediatric recipients of UCBT, we assessed immune cell recovery and immunoglobulin reconstitution at days +100, 180 and 365 and analysed risk factors associated with acute and chronic GVHD. Immune cell subset recovery, immunoglobulin reconstitution, and the incidence of opportunistic infections did not differ significantly between MAC versus RTC groups. In a Cox model, MAC versus RTC recipients had significantly higher risk of grade II–IV acute GVHD [Hazard Ratio (HR) 6·1, P = 0·002] as did recipients of 4/6 vs. 5–6/6 HLA‐matched UCBT (HR 3·1, P = 0·03), who also had significantly increased risk of chronic GVHD (HR 18·5, P = 0·04). In multivariate analyses, MAC versus RTC was furthermore associated with significantly increased transplant‐related (Odds Ratio 26·8, P = 0·008) and overall mortality (HR = 4·1, P = 0·0001). The use of adoptive cellular immunotherapy to accelerate immune reconstitution and prevent and treat opportunistic infections and malignant relapse following UCBT warrants further investigation.

Review: Current clinical applications of chimeric antigen receptor (CAR) modified T cells.

The past several years have been marked by extraordinary advances in clinical applications of immunotherapy. In particular, adoptive cellular therapy utilizing chimeric antigen receptor (CAR)-modified T cells targeted to CD19 has demonstrated substantial clinical efficacy in children and adults with relapsed or refractory B-cell acute lymphoblastic leukemia (B-ALL) and durable clinical benefit in a smaller subset of patients with relapsed or refractory chronic lymphocytic leukemia (CLL) or B-cell non-Hodgkin lymphoma (B-NHL). Early-phase clinical trials are currently assessing CAR T-cell safety and efficacy in additional malignancies. Here, we discuss clinical results from the largest series to date investigating CD19-targeted CAR T cells in B-ALL, CLL, and B-NHL, including discussion of differences in CAR T-cell design and production and treatment approach, as well as clinical efficacy, nature of severe cytokine release syndrome and neurologic toxicities, and CAR T-cell expansion and persistence. We additionally review the current and forthcoming use of CAR T cells in multiple myeloma and several solid tumors and highlight challenges and opportunities afforded by the current state of CAR T-cell therapies, including strategies to overcome inhibitory aspects of the tumor microenvironment and enhance antitumor efficacy.

T cell depletion utilizing CD34+ stem cell selection and CD3+ addback from unrelated adult donors in paediatric allogeneic stem cell transplantation recipients

CD34‐selected haploidentical and unrelated donor allogeneic stem cell transplantation (AlloSCT) in paediatric recipients is associated with sustained engraftment and low risk of acute graft‐versus‐host disease (aGVHD), but limited by delayed immune reconstitution and increased risk of viral and fungal infection. The optimal dose of donor T cells to prevent graft failure and minimize risk of early opportunistic infection and post‐transplant lymphoproliferative disorder (PTLD), while avoiding severe aGVHD, remains unknown. We prospectively studied CD34‐selected 8–10/10 human leucocyte antigen (HLA)‐matched unrelated donor (MUD) peripheral blood stem cell transplantation (PBSCT) in a cohort of 19 paediatric AlloSCT recipients with malignant (n = 13) or non‐malignant (n = 6) diseases. T cells were added back to achieve total dose 1·0–2·5 × 105 CD3+/kg. GVHD pharmacoprophylaxis consisted only of tacrolimus. All patients engrafted neutrophils. Probabilities of grade II–IV aGVHD, limited chronic GVHD (cGVHD), and extensive cGVHD were 15·8%, 23·3%, and 0%, respectively. One patient developed PTLD. One‐year infection‐related mortality was 5·6%. T cell immune reconstitution was delayed. One‐year overall survival was 82·3%. Five patients with malignant disease ultimately died from progressive disease. CD34‐selected MUD PBSCT using a defined dose of T cell add‐back resulted in high rates of engraftment and low risk of grade II–IV aGVHD, early transplantation‐related mortality, and extensive cGVHD.

Rituximab pharmacokinetics in children and adolescents with de novo intermediate and advanced mature B-cell lymphoma/leukaemia: a Children's Oncology Group report.

The ANHL01P1 trial was undertaken to determine pharmacokinetics and safety following the addition of rituximab to French‐American‐British/Lymphome Malins de Burkitt (FAB/LMB96) chemotherapy in 41 children and adolescents with Stage III/IV mature B‐cell lymphoma/leukaemia. Patients received rituximab (375 mg/m2) days −2 and 0 of two induction cycles and day 0 of two consolidation cycles. Highest peak levels were achieved following the second dose of each induction cycle [299 ± 19 and 384 ± 25 μg/ml (Group‐B); 245 ± 31 and 321 ± 32 μg/ml (Group‐C)] with sustained troughs and t½ of 26–29 d. Rituximab can be safely added to FAB chemotherapy with high early rituximab peak/trough levels and a long t½.

Overall survival among older U.S. adults with ALL remains low despite modest improvement since 1980: SEER analysis

To the editor: Over the past 4 decades, outcomes have improved dramatically among pediatric patients with acute lymphoblastic leukemia (ALL), with observed cure rates now >80% in developed countries.[1][1] This progress can be attributed, in part, to large cooperative group studies, advances in

Reduced Toxicity Conditioning and Allogeneic Hematopoietic Progenitor Cell Transplantation for Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa is a severe, incurable, inherited blistering disease caused by COL7A1 mutations. Emerging evidence suggests hematopoietic progenitor cells (HPCs) can be reprogrammed into skin; HPC-derived cells can restore COL7 expression in COL7-deficient mice. We report two children with recessive dystrophic epidermolysis bullosa treated with reduced-toxicity conditioning and HLA-matched HPC transplantation.

Pilot Trial of Risk-Adapted Cyclophosphamide Intensity Based Conditioning and HLA Matched Sibling and Unrelated Cord Blood Stem Cell Transplantation in Newly Diagnosed Pediatric and Adolescent Recipients with Acquired Severe Aplastic Anemia

Cyclophosphamide‐based conditioning regimens and allogeneic hematopoietic stem cell transplantation (AlloHSCT) from matched related donors (MRD) has resulted in the highest survival rates in children and adolescents with acquired severe aplastic anemia (SAA). Time to transplant has consistently been associated with decreased overall survival. Reduced toxicity conditioning and AlloHSCT has been used successfully in other pediatric non‐malignant diseases.