Clinical and functional spectrum of RAC2-related immunodeficiency.

ABSTRACT: Mutations in the small Rho-family guanosine triphosphate hydrolase RAC2, critical for actin cytoskeleton remodeling and intracellular signal transduction, are associated with neonatal severe combined immunodeficiency (SCID), infantile neutrophilic disorder resembling leukocyte adhesion deficiency (LAD), and later-onset combined immune deficiency (CID). We investigated 54 patients (23 previously reported) from 37 families yielding 15 novel RAC2 missense mutations, including one present only in homozygosity. Data were collected from referring physicians and literature reports with updated clinical information. Patients were grouped by presentation: neonatal SCID (n = 5), infantile LAD-like disease (n = 5), or CID (n = 44). Disease correlated to RAC2 activity: constitutively active RAS-like mutations caused neonatal SCID, dominant-negative mutations caused LAD-like disease, whereas dominant-activating mutations caused CID. Significant T- and B-lymphopenia with low immunoglobulins were seen in most patients; myeloid abnormalities included neutropenia, altered oxidative burst, impaired neutrophil migration, and visible neutrophil macropinosomes. Among 42 patients with CID with clinical data, upper and lower respiratory infections and viral infections were common. Twenty-three distinct RAC2 mutations, including 15 novel variants, were identified. Using heterologous expression systems, we assessed downstream effector functions including superoxide production, p21-activated kinase 1 binding, AKT activation, and protein stability. Confocal microscopy showed altered actin assembly evidenced by membrane ruffling and macropinosomes. Altered protein localization and aggregation were observed. All tested RAC2 mutant proteins exhibited aberrant function; no single assay was sufficient to determine functional consequence. Most mutants produced elevated superoxide; mutations unable to support superoxide formation were associated with bacterial infections. RAC2 mutations cause a spectrum of immune dysfunction, ranging from early onset SCID to later-onset combined immunodeficiencies depending on RAC2 activity. This trial was registered at www.clinicaltrials.gov as #NCT00001355 and #NCT00001467.

COVID-19 Vaccination in Patients with Inborn Errors of Immunity Reduces Hospitalization and Critical Care Needs Related to COVID-19: a USIDNET Report.

BACKGROUND: The CDC and ACIP recommend COVID-19 vaccination for patients with inborn errors of immunity (IEI). Not much is known about vaccine safety in IEI, and whether vaccination attenuates infection severity in IEI. OBJECTIVE: To estimate COVID-19 vaccination safety and examine effect on outcomes in patients with IEI. METHODS: We built a secure registry database in conjunction with the US Immunodeficiency Network to examine vaccination frequency and indicators of safety and effectiveness in IEI patients. The registry opened on January 1, 2022, and closed on August 19, 2022. RESULTS: Physicians entered data on 1245 patients from 24 countries. The most common diagnoses were antibody deficiencies (63.7%). At least one COVID-19 vaccine was administered to 806 patients (64.7%), and 216 patients received vaccination prior to the development of COVID-19. The most common vaccines administered were mRNA-based (84.0%). Seventeen patients were reported to seek outpatient clinic or emergency room care for a vaccine-related complication, and one patient was hospitalized for symptomatic anemia. Eight hundred twenty-three patients (66.1%) experienced COVID-19 infection. Of these, 156 patients required hospitalization (19.0%), 47 required ICU care (5.7%), and 28 died (3.4%). Rates of hospitalization (9.3% versus 24.4%, p < 0.001), ICU admission (2.8% versus 7.6%, p = 0.013), and death (2.3% versus 4.3%, p = 0.202) in patients who had COVID-19 were lower in patients who received vaccination prior to infection. In adjusted logistic regression analysis, not having at least one COVID-19 vaccine significantly increased the odds of hospitalization and ICU admission. CONCLUSION: Vaccination for COVID-19 in the IEI population appears safe and attenuates COVID-19 severity.

The impact of institutional measures on optimal use of intravenous immunoglobulin.

BACKGROUND: Intravenous immunoglobulin (IVIG) shortage represents an emerging issue in transfusion medicine. Limited data are available to determine effective strategies for optimal use. The objective of this retrospective observational study was to determine the impact of institutional measures on IVIG use at a large academic center. METHODS: IVIG infusions from November 26, 2018 to September 25, 2022 were categorized according to their appropriateness (Recommended, Option of treatment, or Unrecommended), based on provincial guidelines, and separated into three phases: Reference, Transition, and Post-Implementation phases, the latter following the adoption of restrictive measures, including mandatory standardized order forms, a blood bank gatekeeping strategy, and the creation of a stewardship committee. RESULTS: A total of 5431 IVIG infusions were administered to 544 patients, accounting for 295,033 g. The most common indication categories were neurology (30.4%), immunology (29.0%), and hematology (17.4%). From Reference to Post-Implementation phase, IVIG infusions decreased from 2275 to 2000 with unrecommended indications dropping from 9.5% to 7.4% (p = 0.01), and a global reduction of 23.0% (from 131,163 g to 100,936 g of IVIG). Decrease in chronic immunomodulation accounted for 48.3% of total reduction (14,610 g of 30,227 g), whereas single-use immunomodulation, 40.5% (12,237 g of 30,227 g). Moreover, an absolute reduction of 16.9% was observed in orders exceeding the recommended doses (20.8% to 3.9%; p < 0.0001). Together, the unrecommended and excessive IVIG doses decreased from 19,975 g (15.2%) to 6670 g (6.6%). CONCLUSIONS: A global reduction in IVIG use and a preferential decrease in the unrecommended orders were observed, most likely attributable to the bundle of restrictive strategies implemented.

Real-World Effectiveness of Nirmatrelvir/Ritonavir on Coronavirus Disease 2019-Associated Hospitalization Prevention: A Population-based Cohort Study in the Province of Quebec, Canada.

BACKGROUND: Nirmatrelvir/ritonavir has shown to reduce COVID-19 hospitalization and death before Omicron, but updated real-world evidence studies are needed. This study aimed to assess whether nirmatrelvir/ritonavir reduces the risk of COVID-19-associated hospitalization among high-risk outpatients. METHODS: A retrospective cohort study of outpatients with SARS-CoV-2 between March 15 and 15 October 2022, using data from the Quebec clinico-administrative databases. Outpatients treated with nirmatrelvir/ritonavir were compared with infected ones not receiving nirmatrelvir/ritonavir using propensity-score matching. Relative risk (RR) of COVID-19-associated hospitalization within 30 days was assessed using a Poisson regression. RESULTS: A total of 8402 treated outpatients were matched to controls. Regardless of vaccination status, nirmatrelvir/ritonavir treatment was associated with a 69% reduced RR of hospitalization (RR: .31; 95% CI: .28; .36; number needed to treat [NNT] = 13). The effect was more pronounced in outpatients with incomplete primary vaccination (RR: .04; 95% CI: .03; .06; NNT = 8), while no benefit was found in those with a complete primary vaccination (RR: .93; 95% CI: .78; 1.08). Subgroups analysis among high-risk outpatients with a complete primary vaccination showed that nirmatrelvir/ritonavir treatment was associated with a significant decrease in the RR of hospitalization in severely immunocompromised outpatients (RR: .66; 95% CI: .50; .89; NNT = 16) and in high-risk outpatients aged ≥70 years (RR: .50; 95% CI: .34; .74; NNT = 10) when the last dose of the vaccine was received at least 6 months ago. CONCLUSIONS: Nirmatrelvir/ritonavir reduces the risk of COVID-19-associated hospitalization among incompletely vaccinated high-risk outpatients and among some subgroups of completely vaccinated high-risk outpatients.

Therapeutic options for CTLA-4 insufficiency.

BACKGROUND: Heterozygous germline mutations in cytotoxic T lymphocyte-associated antigen-4 (CTLA4) impair the immunomodulatory function of regulatory T cells. Affected individuals are prone to life-threatening autoimmune and lymphoproliferative complications. A number of therapeutic options are currently being used with variable effectiveness. OBJECTIVE: Our aim was to characterize the responsiveness of patients with CTLA-4 insufficiency to specific therapies and provide recommendations for the diagnostic workup and therapy at an organ-specific level. METHODS: Clinical features, laboratory findings, and response to treatment were reviewed retrospectively in an international cohort of 173 carriers of CTLA4 mutation. Patients were followed between 2014 and 2020 for a total of 2624 months from diagnosis. Clinical manifestations were grouped on the basis of organ-specific involvement. Medication use and response were recorded and evaluated. RESULTS: Among the 173 CTLA4 mutation carriers, 123 (71%) had been treated for immune complications. Abatacept, rituximab, sirolimus, and corticosteroids ameliorated disease severity, especially in cases of cytopenias and lymphocytic organ infiltration of the gut, lungs, and central nervous system. Immunoglobulin replacement was effective in prevention of infection. Only 4 of 16 patients (25%) with cytopenia who underwent splenectomy had a sustained clinical response. Cure was achieved with stem cell transplantation in 13 of 18 patients (72%). As a result of the aforementioned methods, organ-specific treatment pathways were developed. CONCLUSION: Systemic immunosuppressants and abatacept may provide partial control but require ongoing administration. Allogeneic hematopoietic stem cell transplantation offers a possible cure for patients with CTLA-4 insufficiency.

Phenotype, penetrance, and treatment of 133 cytotoxic T-lymphocyte antigen 4-insufficient subjects.

BACKGROUND: Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is a negative immune regulator. Heterozygous CTLA4 germline mutations can cause a complex immune dysregulation syndrome in human subjects. OBJECTIVE: We sought to characterize the penetrance, clinical features, and best treatment options in 133 CTLA4 mutation carriers. METHODS: Genetics, clinical features, laboratory values, and outcomes of treatment options were assessed in a worldwide cohort of CTLA4 mutation carriers. RESULTS: We identified 133 subjects from 54 unrelated families carrying 45 different heterozygous CTLA4 mutations, including 28 previously undescribed mutations. Ninety mutation carriers were considered affected, suggesting a clinical penetrance of at least 67%; median age of onset was 11 years, and the mortality rate within affected mutation carriers was 16% (n = 15). Main clinical manifestations included hypogammaglobulinemia (84%), lymphoproliferation (73%), autoimmune cytopenia (62%), and respiratory (68%), gastrointestinal (59%), or neurological features (29%). Eight affected mutation carriers had lymphoma, and 3 had gastric cancer. An EBV association was found in 6 patients with malignancies. CTLA4 mutations were associated with lymphopenia and decreased T-, B-, and natural killer (NK) cell counts. Successful targeted therapies included application of CTLA-4 fusion proteins, mechanistic target of rapamycin inhibitors, and hematopoietic stem cell transplantation. EBV reactivation occurred in 2 affected mutation carriers after immunosuppression. CONCLUSIONS: Affected mutation carriers with CTLA-4 insufficiency can present in any medical specialty. Family members should be counseled because disease manifestation can occur as late as 50 years of age. EBV- and cytomegalovirus-associated complications must be closely monitored. Treatment interventions should be coordinated in clinical trials.

DRESS syndrome: cerebral vasculitic-like presentation.

INTRODUCTION: DRESS (drug reaction with eosinophilia and systemic symptoms) syndrome is a severe adverse drug-induced reaction. It manifests with pyrexia, eosinophilia, and lymphadenopathy, with multiple organ involvement, mainly the skin, liver, and kidneys. The purpose of this article is to demonstrate that DRESS syndrome can be associated with cerebral manifestations, a concept not well known in the neuroradiological literature. METHODS: We describe three cases of DRESS syndrome associated with cerebral vasculitic-like lesions and realize a review of the literature to demonstrate that this association represents a very rare entity. RESULTS: Acute ischemic lesions were found among two patients. In all cases, perivascular enhancement was present. Magnetic resonance angiography (MRA) sequence was normal. Although no cerebral biopsy was performed, this enhancement pattern is strongly suggestive of a vasculitic process associated with DRESS syndrome. CONCLUSION: Diagnosis of cerebral vasculitic-like associated lesions must be considered in patients with DRESS syndrome since it can be reversed completely by withdrawing the causal medication and instigating corticosteroid treatment in a timely fashion.

Increase in de novo food allergies after pediatric liver transplantation: tacrolimus vs. cyclosporine immunosuppression.

Post-TAFA is an uncommon but serious complication of organ transplantation. This study aimed to compare the incidence of FA in CsA and tacrolimus-treated children following OLT and identify risk factors. The medical charts of all patients who underwent OLT at our institution were reviewed. Between 1985 and 2010, 218 OLTs were performed on 188 pediatric recipients, of which 154 were included in the study. Three patients (3%) of the 102 receiving CsA developed FA, compared with nine (17%) in the 52 tacrolimus-treated patients, the latter exceeding general population reported FA prevalence (RR 5.88; 95% CI: 1.66-20.81). All TAFA cases underwent transplantation before the age of three with an incidence of 29% (9/31) in the tacrolimus-treated children in comparison with 7% (3/41) in the CsA group (RR 3.97; 95% CI: 1.17-13.45). Eosinophilia was present in 81% of children receiving tacrolimus compared with 54% in the CsA group (p = 0.002). We observed a statistically significant increase incidence of FA in tacrolimus-treated children following an OLT and those under the age of three are particularly vulnerable. The underlying process is still unknown and probably multifactorial.

The Disease Burden of Hereditary Angioedema: Insights from a Survey in French-Canadians from Quebec.

Background: Limited data are available on the clinical profile and disease burden of hereditary angioedema (HAE) in Canadians. Objective: This study aimed to assess HAE disease characteristics and the burden of disease in Canadians with HAE types I, II, and normal levels of C1 inhibitor (nC1-INH). Materials and Methods: A 46-item patient survey evaluating clinical characteristics and burden of disease was developed and disseminated by the HAE patient organization Angio-oédeme héréditaire du Québec in Quebec, Canada, from May 2019 to February 2020. The survey received Research Review Board ethics approval. Results: In the 35 respondents, HAE type I was the most common (46%), followed by nC1-INH (43%). Female participants were significantly younger at first symptom presentation than males (p=0.04). Prior to diagnosis, 69% of participants underwent unnecessary treatments and procedures, with a 10-year delay between first symptoms and diagnosis. Before starting the current treatment, 42% of participants experienced weekly HAE attacks. Most participants identified experiencing attacks in the abdomen (89%), followed by the larynx (66%), feet (66%), hands (63%), and face (63%). Most attacks were severe or moderate, yet almost half of patients waited >1 hr before getting medical attention at their last emergency department (ED) visit. HAE was associated with decreased health-related quality of life, leading to significant functional impairment in personal and professional life. As compared to HAE type I/II, patients with HAE nC1-INH were treated more often with tranexamic acid for long-term prophylaxis, and their condition was less controlled, resulting in more attacks and ED visits. Conclusion: HAE manifests in this patient population as frequent moderate-to-severe attacks and a high disease burden; the HAE subtype may differentially affect care requirements. There is an urgent need for increased awareness and education on HAE among treating physicians.

Severe Relapsing Autoimmune Encephalitis with GABAA Receptor, Titin, and AchR Antibodies in a Patient with Thymoma: A Case Report.

Introduction: We report a challenging case of autoimmune encephalitis in a patient with a thymoma harboring titin and acetylcholine receptor antibodies, who experienced multiple relapses despite thymectomy and aggressive first-line immunotherapy, and for whom GABAA receptor antibodies were ultimately identified. Case Presentation: This 40-year-old man presented with headaches, weakness, diplopia, hearing loss, and seizures progressing to status epilepticus. Brain MRI showed multifocal cortical and subcortical T2/fluid attenuated inversion recovery hyperintense lesions without enhancement. Initial neural antibody testing identified only acetylcholine receptor and titin antibodies. He presented multiple severe relapses despite complete thymoma resection, intravenous methylprednisolone with immunoglobulins or plasmapheresis, and mycophenolate mofetil. Second-line immunotherapy with rituximab was successful to alleviate symptoms and normalize the EEG and MRI after identification of anti-GABAA receptor antibodies on more comprehensive neural antibody testing for autoimmune encephalitis. Conclusion: This case demonstrates the complexity and importance of identifying pathogenic antibodies and selecting 2nd line treatment accordingly in patients with autoimmune encephalitis when multiple antibodies coexist. Despite tumor resection, aggressive immunotherapy may be needed to prevent further deterioration in anti-GABAA receptor encephalitis.

Revaccination outcomes among adolescents and adults with suspected hypersensitivity reactions following COVID-19 vaccination: A Canadian immunization research network study.

BACKGROUND: COVID-19 vaccination has been associated with anaphylaxis and hypersensitivity reactions. Infectious disease physicians and allergists in the Canadian Special Immunization Clinic (SIC) Network developed guidance for evaluating patients with adverse events following immunization (AEFI) including suspected hypersensitivity. This study evaluated management and adverse event recurrence following subsequent COVID-19 vaccinations. METHODS: Individuals aged 12 years and older enrolled at participating SICs before February 28, 2023 who were referred for suspected or diagnosed hypersensitivity reaction following COVID-19 vaccination, or for prevaccination assessment of suspected allergy to a COVID-19 vaccine component were included. De-identified clinical assessments and revaccination data, captured in a centralized database, were analyzed. The Brighton Collaboration case definition (BCCD) for anaphylaxis (2023 version) was applied. RESULTS: The analysis included 206 participants from 13 sites: 26 participants referred for pre-vaccination assessment and 180 participants referred for adverse events following COVID-19 vaccination (15/180 [8.3%] with BCCD confirmed anaphylaxis, 84 [46.7%] with immediate hypersensitivity symptoms not meeting BCCD, 33 [18.3%] with other diagnosed hypersensitivity reactions, and 48 [26.7%] participants with a final diagnosis of non-hypersensitivity AEFI). Among participants referred for AEFIs following COVID-19 vaccination, 166/180 (92.2%) were recommended for COVID-19 revaccination after risk assessment, of whom 158/166 (95.2%) were revaccinated (all with a COVID-19 mRNA vaccine). After revaccination, 1/15 (6.7%) participants with prior anaphylaxis, 1/77 (1.3%) with immediate hypersensitivity not meeting criteria for anaphylaxis and 1/24 (4.2%) with other physician diagnosed hypersensitivity developed recurrent AEFI symptoms that met the BCCD for anaphylaxis. All 26 participants referred pre-vaccination, including 9 (34.6%) with history of polyethylene glycol-asparaginase reactions, were vaccinated without occurrence of immediate hypersensitivity symptoms. CONCLUSIONS: Most individuals in this national cohort who experienced a hypersensitivity event following COVID-19 vaccination and were referred for specialist review were revaccinated without AEFI recurrence, suggesting that specialist evaluation can facilitate safe revaccination.

Transitioning from pediatric to adult healthcare with an inborn error of immunity: a qualitative study of the lived experience of youths and their families.

Introduction: Transition from pediatric to adult healthcare is a multifaceted and consequential process with important health implications for youth. Although research on transition has grown significantly, research on transition for patients living with an inborn error of immunity (IEI) is scarce. We undertook a qualitative study to better understand the perspectives of youths and parents in an outpatient immunology clinic. Methdos: Semi-structured interviews were conducted with 9 youths, 6 parents and 5 clinicians, all recruited from the same clinic. All youths recently transferred to adult care with or without an established diagnosis of IEI. Interviews were transcribed verbatim and thematic analysis was conducted. Two sets of themes were generated. The first set captured the positive and negative aspects experienced during transition, as well as recommendations to facilitate the process. The second set focused on key topics discussed in the interviews that were merged into overarching themes. Results: Perspectives of participants were clustered into 6 overarching themes: (1) lack of knowledge about IEIs; (2) scattered transitions; (3) changing healthcare teams; (4) approaching an unknown environment; (5) transitioning to adulthood; (6) assuming responsibility for the management of the condition. Overall, the challenges encountered with respect to these themes had profound clinical and humanistic implications for patients such as generating significant distress. Discussion: We discuss the unique challenges of the youths in our study in comparison to common problems reported by youths with chronic illness in the broader transition literature (for example: the change of healthcare team, the lack of information about the transition process and navigating the adult care system, growth towards self-management and the co-occurring developmental transition to adulthood). There is an urgency to attend to the specific problems created by the rarity of IEIs and related lack of knowledge about them as well as the need for multidisciplinary cross-clinic care during transition and beyond.

A unique presentation of NLRP3-associated autoinflammatory disease: case report.

BACKGROUND: NLRP3-associated autoinflammatory diseases (NLRP3-AID) are rare genetic autoinflammatory diseases characterized by chronic inflammation and an urticaria-like rash. We report an unusual presentation of severe NLRP3-AID resulting in a significant diagnostic delay of more than three decades. CASE PRESENTATION: The patient presented with early-onset serositis as well as prominent peripheral eosinophilia with organ infiltration, in the absence of the classic urticaria-like rash. DNA analysis by next generation sequencing revealed a sporadic class 4 mutation c.1991T > C (p.Met662Thr) in the NLRP3 gene, confirming a diagnosis of NLRP3-AID at 36 years old. Although treatment with anti-interleukin 1 agent led to clinical remission, irreversible sequelae, namely intellectual disability and deafness, remained. CONCLUSION: This case highlights unique manifestations of NLRP3-AID, namely the absence of urticaria-like rash, eosinophilic organ infiltration, and pseudoseptic serositis. In order to avoid diagnostic delay and its dire consequences, NLRP3-AID should be suspected in patients displaying autoinflammatory features combined with serum and tissue eosinophilia and/or marked serositis, regardless of skin involvement.

Acute central nervous system graft-versus-host-disease after liver transplantation.

Acute Central Nervous System (CNS) Graft Versus Host Disease (GvHD) is a rare form of GvHD, only described in case reports. Knowledge about this condition is extrapolated from chronic CNS GvHD cases occurring mostly after hematopoietic stem cell transplantation. GvHD following solid organ transplantation is an unexpected complication. GvHD after liver transplantation has a poor prognosis, and the optimal management is not yet known. Here we describe the case of a 63-year-old man who underwent deceased donor liver transplantation and subsequently developed skin rash, colitis and pancytopenia followed by refractory status epilepticus. Following the identification of lymphocytes of donor origin in the cerebrospinal fluid of the patient, he was diagnosed with acute CNS GvHD. He was treated with an intensive immunosuppressive regimen, but care was withdrawn due to lack of improvement and worsening neurologic prognosis. It is the second known case of acute CNS GvHD following liver transplantation. Clinicians should be aware of this possible, although rare, complication of liver transplantation, especially when there is refractory status epilepticus of unknown origin.

Chronic granulomatous disease presenting at age 52 with fulminant mulch pneumonitis.

Chronic granulomatous disease should be considered in adults of any age in the presence of refractory and/or atypical or fulminant pulmonary infections. This case of new large deletions in NCF1 was presented with mulch pneumonitis without a significant history of infections.

Bradykinin-induced angioedema in the emergency department.

BACKGROUND: Acute airway angioedema commonly occurs through two distinct mechanisms: histamine- and bradykinin-dependent. Although they respond to distinct treatments, these two potentially life-threatening states present similarly. Poor recognition of the bradykinin-dependent pathway leads to treatment errors in the emergency department (ED), despite the availability of multiple pharmacologic options for hereditary angioedema (HAE) and other forms of bradykinin-induced angioedema. Here, we consider the pathophysiology and clinical features of bradykinin-induced angioedema, and we present a systematic literature review exploring the effectiveness of the available therapies for managing such cases. METHODS: PubMed searches using 'emergency', 'bradykinin' and various therapeutic product names identified studies reporting the efficacy of treatments for bradykinin-induced angioedema in the ED setting. In all, 22 studies met prespecified criteria and are analysed here. FINDINGS: Whereas histamine-induced angioedema has a faster onset and often presents with urticaria, bradykinin-induced angioedema is slower in onset, with greater incidence of abdominal symptoms. Acute airway angioedema in the ED should initially be treated with anaphylactic protocols, focusing on airway management and treatment with epinephrine, antihistamine and systemic steroids. Bradykinin-induced angioedema should be considered if this standard treatment is not effective, despite proper dosing and regard of beta-adrenergic blockade. Therapeutics currently approved for HAE appear as promising options for this and other forms of bradykinin-induced angioedema encountered in the ED. CONCLUSION: Diagnostic algorithms of bradykinin-induced angioedema should be followed in the ED, with early use of approved therapies to improve patient outcomes.

Population pharmacokinetic analysis of weekly and biweekly IgPro20 (Hizentra®) dosing in patients with primary immunodeficiency.

BACKGROUND: IgPro20 (Hizentra®), a 20% subcutaneous immunoglobulin G (IgG), is an effective treatment for patients with primary immunodeficiencies with impaired IgG production. Flexible dosing regimens of IgPro20 have been supported by pharmacokinetic (PK) modeling and simulation. This study further describes the PK characteristics of serum IgG concentrations after weekly and biweekly administration of IgPro20 and compares predicted and actual serum IgG data using a previously-developed population PK (popPK) model. METHODS: A popPK model was developed by combining data from a previously-published model with data from a Phase 4 study (IgPro20_4005). An external validation of the original model using dosing, demographics, and historic endogenous serum IgG concentrations from patients enrolled in study IgPro20_4005 was performed. This dataset was then simulated 300 times and predicted serum IgG PK characteristics compared with the observed data. RESULTS: A total of 173 patients (156 unique patients from original model and 17 patients from study IgPro20_4005) provided 4078 observations of serum IgG concentrations. The popPK estimates obtained demonstrated a clearance (% inter-individual variability) of 0.138 L/day (35%), volume of central compartment of 3.95 L (78.6%), inter-compartmental clearance of 0.260 L/day (56%), and volume of peripheral compartment of 4.44 L. Validation results indicated that observed serum IgG concentration vs time data fell within the 90% prediction intervals for median, 25th, and 75th percentiles of the simulated IgG concentration time courses. CONCLUSIONS: The present analysis validated the ability of the previously published popPK model to predict serum IgG concentration time profiles after biweekly subcutaneous IgPro20 administration.

Partial Purine Nucleoside Phosphorylase Deficiency Helps Determine Minimal Activity Required for Immune and Neurological Development.

Introduction: Complete or near complete absence of the purine nucleoside phosphorylase (PNP) enzyme causes a profound T cell immunodeficiency and neurological abnormalities that are often lethal in infancy and early childhood. We hypothesized that patients with partial PNP deficiency, characterized by a late and mild phenotype due to residual PNP enzyme, would provide important information about the minimal PNP activity needed for normal development. Methods: Three siblings with a homozygous PNP gene mutation (c.769C>G, p.His257Asp) resulting in partial PNP deficiency were investigated. PNP activity was semi-quantitively assayed by the conversion of [14C]inosine in hemolysates, mononuclear cells, and lymphoblastoid B cells. PNP protein expression was determined by Western Blotting in lymphoblastoid B cells. DNA repair was quantified by measuring viability of lymphoblastoid B cells following ionizing irradiation. Results: A 21-year-old female was referred for recurrent sino-pulmonary infections while her older male siblings, aged 25- and 28- years, did not suffer from significant infections. Two of the siblings had moderately reduced numbers of T, B, and NK cells, while the other had near normal lymphocyte subset numbers. T cell proliferations were normal in the two siblings tested. Hypogammaglobulinemia was noted in two siblings, including one that required immunoglobulin replacement. All siblings had typical (normal) neurological development. PNP activity in various cells from two patients were 8-11% of the normal level. All siblings had normal blood uric acid and increased PNP substrates in the urine. PNP protein expression in cells from the two patients examined was similar to that observed in cells from healthy controls. The survival of lymphoblastoid B cells from 2 partial PNP-deficient patients after irradiation was similar to that of PNP-proficient cells and markedly higher than the survival of cells from a patient with absent PNP activity or a patient with ataxia telangiectasia. Conclusions: Patients with partial PNP deficiency can present in the third decade of life with mild-moderate immune abnormalities and typical development. Near-normal immunity might be achieved with relatively low PNP activity.