Multidimensional Response Surface Methodology for the Development of a Gene Editing Protocol for p67phox-Deficient Chronic Granulomatous Disease

Replacing a faulty gene with a correct copy has become a viable therapeutic option as a result of recent progress in gene editing protocols. Targeted integration of therapeutic genes in hematopoietic stem cells has been achieved for multiple genes using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 system and Adeno-Associated Virus (AAV) to carry a donor template. Although this is a promising strategy to correct genetic blood disorders, it is associated with toxicity and loss of function in CD34+ hematopoietic stem and progenitor cells, which has hampered clinical application. Balancing the maximum achievable correction against deleterious effects on the cells is critical. However, multiple factors are known to contribute, and the optimization process is laborious and not always clearly defined. We have developed a flexible multidimensional Response Surface Methodology approach for optimization of gene correction. Using this approach, we could rapidly investigate and select editing conditions for CD34+ cells with the best possible balance between correction and cell/colony-forming unit (CFU) loss in a parsimonious one-shot experiment. This method revealed that using relatively low doses of AAV2/6 and CRISPR/Cas9 ribonucleoprotein complex, we can preserve the fitness of CD34+ cells and, at the same time, achieve high levels of targeted gene insertion. We then used these optimized editing conditions for the correction of p67phox-deficient chronic granulomatous disease (CGD), an autosomal recessive disorder of blood phagocytic cells resulting in severe recurrent bacterial and fungal infections and achieved rescue of p67phox expression and functional correction of CD34+-derived neutrophils from a CGD patient.

Hematopoietic stem cell gene editing rescues B-cell development in X-linked agammaglobulinemia

BACKGROUND

X-linked agammaglobulinemia (XLA) is an inborn error of immunity that renders boys susceptible to life-threatening infections due to loss of mature B cells and circulating immunoglobulins. It is caused by defects in the gene encoding the Bruton tyrosine kinase (BTK) that mediates the maturation of B cells in the bone marrow and their activation in the periphery. This paper reports on a gene editing protocol to achieve "knock-in" of a therapeutic BTK cassette in hematopoietic stem and progenitor cells (HSPCs) as a treatment for XLA.

METHODS

To rescue BTK expression, this study employed a clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 system that creates a DNA double-strand break in an early exon of the BTK locus and an adeno-associated virus 6 virus that carries the donor template for homology-directed repair. The investigators evaluated the efficacy of the gene editing approach in HSPCs from patients with XLA that were cultured in vitro under B-cell differentiation conditions or that were transplanted in immunodeficient mice to study B-cell output in vivo.

RESULTS

A (feeder-free) B-cell differentiation protocol was successfully applied to blood-mobilized HSPCs to reproduce in vitro the defects in B-cell maturation observed in patients with XLA. Using this system, the investigators could show the rescue of B-cell maturation by gene editing. Transplantation of edited XLA HSPCs into immunodeficient mice led to restoration of the human B-cell lineage compartment in the bone marrow and immunoglobulin production in the periphery.

CONCLUSIONS

Gene editing efficiencies above 30% could be consistently achieved in human HSPCs. Given the potential selective advantage of corrected cells, as suggested by skewed X-linked inactivation in carrier females and by competitive repopulating experiments in mouse models, this work demonstrates the potential of this strategy as a future definitive therapy for XLA.

Outcomes following SARS-CoV-2 infection in patients with primary and secondary immunodeficiency in the UK

In March 2020, the United Kingdom Primary Immunodeficiency Network (UKPIN) established a registry of cases to collate the outcomes of individuals with PID and SID following SARS-CoV-2 infection and treatment. A total of 310 cases of SARS-CoV-2 infection in individuals with PID or SID have now been reported in the UK. The overall mortality within the cohort was 17.7% (n = 55/310). Individuals with CVID demonstrated an infection fatality rate (IFR) of 18.3% (n = 17/93), individuals with PID receiving IgRT had an IFR of 16.3% (n = 26/159) and individuals with SID, an IFR of 27.2% (n = 25/92). Individuals with PID and SID had higher inpatient mortality and died at a younger age than the general population. Increasing age, low pre-SARS-CoV-2 infection lymphocyte count and the presence of common co-morbidities increased the risk of mortality in PID. Access to specific COVID-19 treatments in this cohort was limited: only 22.9% (n = 33/144) of patients admitted to the hospital received dexamethasone, remdesivir, an anti-SARS-CoV-2 antibody-based therapeutic (e.g. REGN-COV2 or convalescent plasma) or tocilizumab as a monotherapy or in combination. Dexamethasone, remdesivir, and anti-SARS-CoV-2 antibody-based therapeutics appeared efficacious in PID and SID. Compared to the general population, individuals with PID or SID are at high risk of mortality following SARS-CoV-2 infection. Increasing age, low baseline lymphocyte count, and the presence of co-morbidities are additional risk factors for poor outcome in this cohort.

The first reported cases of meat allergy following tick bites in the UK

Allergic reactions frequently involve the production of immunoglobulin E (IgE) antibodies to proteins. However, reactions directed against carbohydrate moieties are increasingly being recognised. Tick bites can contribute to the development of immunoglobulin E to the galactose-1,3-galactose (alpha-gal) moiety on tick salivary proteins. These IgE molecules can cross-react with alpha-gal found in red meats, causing Type I IgE-mediated hypersensitivity reactions to these foods. We present three cases of delayed reactions to beef, pork and lamb in patients with prior tick bites and in the presence of a positive-specific IgE to alpha-gal. Patients were advised to avoid red meat consumption and to carry emergency treatment in the form of anti-histamines with or without adrenaline autoinjector devices. This is the first published report of red meat allergy caused by tick bites suffered in the UK.

EP34 Assessing the ability of anti-C1q antibody measurement to predict a flare of lupus nephritis

Background

Systemic lupus erythematous (SLE) is a multi-system autoimmune disease which has a relapsing and remitting course. Patients with lupus nephritis (LN) are at risk of relapse and hence long term follow up and disease monitoring are of particular importance. Anti-C1q antibodies (C1Q Ab) are observed in 30-60% of patients with SLE. It has been postulated that the presence of C1Q Ab can predict a flare of LN. Here we undertook a prospective follow up of patients after having a C1Q Ab measurement to determine whether the result predicted a flare of LN.

Methods

SLE patients attending an Inner-City Lupus Center, were involved in the study. All fulfilled the 2012 SLICC criteria for SLE. A point-in-time measurement of C1Q Ab was made using an ELISA kit (Orgentec Diagnostika GmbH). A positive test defined by the manufacturer is a level above 10 U/ml. Medical records of patients were reviewed over the following 1 year to identify LN flares. A renal flare was defined as a doubling of the protein creatinine ratio with a subsequent decision to escalate immunosuppressive therapy. Chi Squared tests were used to assess statistical significance. 9 patients who were being treated for a flare of LN at the time of C1Q Ab were excluded from the analysis.

Results

116 lupus patients were included in the study. Of those, 52 had biopsy proven LN (45%). Positive C1Q ab was more common in patients with a history of biopsy proven LN (n = 17, 32.7%) compared to those with non-renal SLE (n = 10, 15.6%),(p = 0.03). Renal flares tended to be more common in C1q ab positive LN patients (n = 4, 26.7%) compared to those without C1q ab (n = 2, 7.14%). (p = 0.782). Of the 64 patients with non-renal SLE, 1 (10%) C1Q Ab positive patient subsequently developed LN compared with 1 (1.85%) C1Q Ab negative patient (p = 0.173).There was no correlation between the level of C1Q Ab and the rate of LN flares. Having a positive dsDNA antibody level at the time of sampling also did not appear to predict a flare.

Conclusion

C1Q Ab has a known correlation with LN, however its ability to predict flares has been less well characterised. Our prospective analysis shows that although the C1Q Ab positive patients were more likely to have a flare of LN in the following year, there was not a statistically significant difference between the C1Q Ab positive and negative groups. In addition, only a relatively small proportion of C1Q Ab positive patients went on to have a flare (20%). Our data therefore does not support the use of C1Q Ab as a predicting factor for a subsequent flare of LN.

Disclosures

S. Bahal None. D. Pyne None. R. Rajakariar None. M. Lewis None. A. Pakozdi None. A. Cove-Smith None.

Case Report: Resolution of chronic urticaria following treatment of odontogenic infection

Background: Chronic spontaneous urticaria (CSU) is a condition characterised by the presence of hives with/without angioedema, that affects individuals on more days than not for 6 weeks or more. The role of infection as a potential trigger for CSU is well described, but the current clinical guidelines do not recommend routine screening for underlying infections.

Main observations: We report a case of severe prolonged chronic spontaneous urticaria in a 19-year-old, that went into rapid remission following the treatment of dental infection.

Conclusions: Clinicians should recognise the potential role that infection can have in causing chronic urticaria. There should be a low threshold to treat infection in such circumstances.

Anaphylaxis after disinfection with 2% chlorhexidine wand applicator

A 54-year-old man with end-stage renal failure attended for dialysis. Within seconds of applying 2% w/v chlorhexidine (ChloraPrep 3 mL Wand Applicator) to the skin surrounding the insertion point of his dialysis catheter (Tesio catheter), he developed pruritus, urticaria, shortness of breath, hypotension and reduced responsiveness. Treatment for anaphylaxis was initiated with rapid improvement of his symptoms, and he made a full recovery. Allergy to chlorhexidine was confirmed with skin testing, and the patient was warned against all future exposure to chlorhexidine. Subsequent dialysis without chlorhexidine was uneventful.