ABO-incompatible Transplantation Research Articles

#2917 Desensitization techniques in ABO-incompatible renal transplantation: efficacy and analysis of complications

Abstract Background and Aims Living donor transplantation is the best optimal choice for the vast majority of patients with terminal renal insufficiency. However, it is limited by the AB0/ HLA incompatibility between donor and receptor. The resolution of this inconvenient relies on desensitization of isoagglutinins (anti-AB0 immunoglobulins depletion); thus transplantation could be performed safely. For desensitization there are two techniques: specific adsorption (S) and non-specific (NS) techniques, including centrifugal therapeutic plasma exchange (cTPE) and membrane-based therapeutic plasma exchange (mTPE). The aims are to evaluate the efficacy of apheresis techniques: specific versus non-specific, and identify their complications. Secondary objectives include analyzing the acute rejection rate (RR), graft survival, and complications of each technique. Method A retrospective cohort study was conducted on AB0-incompatible living donor transplantation patients at our center (Bellvitge's Hospital) from 2014 to 2022. All patients (except 1) received rituximab and induction treatment by Thymoglobulin or Basiliximab, followed by maintenance treatment (Steroids, Mycophenolate, and calcineurin inhibitors). During follow-up, protocol renal biopsies (RB) were taken at one month and between 3-6 months post-transplantation. Complications were defined as significant haematological alterations, bleeding, or major infections requiring hospitalization. According to the technique used, two cohorts were identified: specific (Glycosorb®/Vitrosorb® columns) and non-specific: mTPE (prismaflex TPE2000) and cTPE (Spectra/Optia®). Both were anticoagulated with heparin or citrate randomly. An expert nurse supervised the technique. To calculate the efficacy we considered the percentual reduction of isoagglutinins in the first session. T-student test was used to calculate the percentage of complication and compare the results. Results A total of 50 patients were selected with a mean age (MA) of 49.5 ± 11.8. Four of these did not require apheresis due to lower title isoagglutinins (<1/8). Each cohort included 23 patients: specific with MA 49.5 vs non-specific 48.4, with a mean isoagglutinin titles in specific of 61.65 vs non-specific 11.8 (p = 0.05). Isoagglutinin clearance were higher in specific techniques with 73% vs 59% non-specific (p < 0.03). Due to the dispersion in the number of sessions, results are expressed with the median (4 sessions in specific vs 3 non-specific). Total renal graft survival rate is 93.4%. At one month, it was diagnosed by biopsy an acute renal rejection rate of 16.7% in non-specific vs 18.2% specific (p > 0.05). Considering complications, they are higher with non-specific 41.7% vs specific 18% (p < 0.05). Regarding infectious issues, there are no differences in cytomegalovirus or polyomavirus infections, but there are differences in urinary infections observing in non-specific 79.2% vs specific 63% (p < 0.05). Conclusion Specific techniques are more effective in reducing isoagglutinins, show a lower rate of complications and post-transplant infections, providing greater benefit to the patient.

Immuno-Hematologic Complexity of ABO-Incompatible Allogeneic HSC Transplantation.

ABO incompatibility is not considered a contraindication for hematopoietic stem cell transplantation (HSCT). Approximately 30% of transplants from related donors and up to 50% of transplants from unrelated donors are ABO incompatible. Immuno-hematologic investigations allow to estimate donor/recipient ABO mismatch and anti-A/B isohemagglutinin (IHA) titration in the pre-HSCT phase. Immediate hemolysis or delayed complications (passenger lymphocyte syndrome and pure red cell aplasia) can occur post HSCT. Some preventive measures take into consideration either decision-making algorithms based on the recipient's IHA titration or clinical protocols for the removal/reduction of IHAs through plasma exchange or immunoadsorption procedures. Product manipulation through red blood cell (RBC) and/or plasma depletion can also be taken into account. Currently, the best approach in the management of ABO-incompatible transplant is not defined in expert consensus documents or with solid evidence. In addition, the methods for IHA titration are not standardized. A transfusion strategy must consider both the donor's and recipient's blood group systems until the RBC engraftment catches on and ABO conversion (forward and reverse typing) is confirmed on two consecutive and independent samples. Therefore, ABO incompatibility in HSCT represents a demanding immuno-hematologic challenge and requires all necessary preventive measures, including the appropriate selection of ABO blood components for transfusion.

The paediatric liver transplant experience in Johannesburg, South Africa: A broad overview and update

Background: The Wits Transplant Unit performed its first paediatric liver transplant in 2005. Initial experiences from the unit were published in 2012 and 2014. Since then, significant progress has been made in capacity-building the unit, improving outcomes and enhancing service delivery. This paper presents a broad overview and update of the unit’s 17-year experience. Methods: We conducted a retrospective review of all paediatric liver transplants performed in Johannesburg from 1 January 2005 to 31 December 2021 with a minimum one-year follow-up. Data were accessed from the Wits Donald Gordon Medical Centre Paediatric Liver Transplant Research Database (University of the Witwatersrand Human Research Ethics approval: M190749). The following data were collected: donor and recipient sociodemographic and clinical characteristics, details of transplant procedures, donor grafts and recipient outcomes (post-operative complications, graft and recipient survival). Results: A total of 270 transplants were performed during the review period. Two thirds of recipients (n=180, 67%) were younger than 5 years at time of transplant and half (n=135, 50%) received a living donor graft. The most common indication for liver transplant was biliary atresia, followed by acute liver failure. Unadjusted recipient survival was 80% (95% CI: 75-85%) at one year, and 68% (95% CI: 59-75%) at five years. Waiting list mortality decreased from 27.3% in 2017 to 5.9% in 2021. One hundred and fifty-four (57.0%) recipients experienced at least one type of intervention requiring surgical complication - the most common being biliary in nature (n = 91; 33.7%). Conclusion: Over last seventeen years, a sustainable paediatric liver transplantation service has been established in Johannesburg. Living donor, split and ABO incompatible liver transplants have been incorporated in response to the severe organ shortage in South Africa. However, our outcomes can be improved. Additionally, a national transplant initiative to coordinate timeous referrals and expand access to liver transplantation for children with severe acute and chronic liver failure is advised.

ABO-incompatible liver transplantation – exploring utilitarian solutions to restricted access and organ shortages: A single-centre experience from Johannesburg, South Africa

Background. Liver transplantation is the definitive management for severe acute liver failure refractory to supportive management, and end- stage chronic liver failure. Owing to a shortage of deceased liver donors, South Africa requires innovative techniques to broaden the donor pool. Objectives. This study evaluated the outcomes of the Wits Transplant Unit ABO-incompatible liver transplant (ABOi-LT) programme. Methods. This retrospective record review compared all adult and paediatric patients receiving ABO-compatible (ABOc) and ABO-incompatible (ABOi) liver transplants from January 2014 to December 2021 with a minimum one-year follow-up. Primary outcomes were recipient and graft survival and secondary outcomes included vascular, enteric and biliary complications, relook surgery, acute cellular rejection (ACR) and lenghth of hospital stay. Cox proportional hazards regression was performed to examine the effect of ABO-compatibility group on recipient and graft survival. The relationship between the ABO-compatibility group and categorical outcomes was assessed by binomial regression. Results. During the study period, 532 liver transplants were performed; 44/532 (8%) were ABOi of which 14/44 (32%) were paediatric and 30/44 (68%) adult recipients. Within the pediatric group, the proportion of transplants performed for acute liver failure was significantly higher in the ABOi group (7/14; 50%) compared with the ABOc group (33/207; 16%) (p=0.005). Comparable recipient and graft survival estimates were noted: one-, three- and five-year recipient survival in the ABOi group was 77% (95% confidence interval (CI) 44 - 92), 58% (95% CI 17 - 84) and 58% (95% CI 17 - 84) respectively. There were significantly increased relative risks of relook surgery for the ABOi group compared with the ABOc group, both overall (relative risk (RR) 1.74; 95% CI 1.10 - 2.75) and at 90 days (RR 2.28; 95% CI 1.27 - 4.11); and also, for pre-discharge bloodstream infection (BSI), (RR 1.84; 95% CI 1.11 - 3.06). In adults, there were significantly more acute indications for liver transplantation in the ABOi (10/30; 33%) compared with the ABOc group (26/281; 9%) (p=0.0007) with the most common cause being drug or toxin ingestion (16/36; 44%). For the ABOi group, recipient survival estimates (95% CI) at 1, 3 and 5 years were 71% (50 - 84), 63% (41 - 78) and 58% (37 - 75) which, as noted with complication rates, were similar between ABO groups. Conclusion. This study confirms ABOi-LT as a feasible option to increase the liver donor pool in this organ-depleted setting as recipient survival and complication rates were similar between ABO-compatibility groups.

Incidence, epidemiology, and outcomes of acute allograft rejection following liver transplantation in Australia.

Acute allograft rejection is a well-known complication of liver transplantation (LT). The incidence, epidemiology, and outcomes of acute rejection have not been well described in Australia. We retrospectively studied consecutive adults who underwent deceased donor LT at a single center between 2010 and 2020. Donor and recipient data at the time of LT and recipient outcomes were collected from a prospective LT database. Liver biopsy reports were reviewed, and only a graft's first instance of biopsy-proven acute rejection was analyzed. During the study period, 796 liver transplants were performed in 770 patients. Biopsy-proven rejection occurred in 34.9% of transplants. There were no significant changes in the incidence of rejection over time (linear trend p =0.11). The median time to the first episode of rejection was 71 days after LT: 2.2% hyperacute, 50.4% early (≤90d), and 47.5% late rejection (>90d). Independent risk factors for rejection were younger recipient age at transplant (aHR 0.98 per year increase, 95% CI: 0.97-1.00, p =0.01), and ABO-incompatible grafts (aHR 2.55 vs. ABO-compatible, 95% CI: 1.27-5.09, p <0.01) while simultaneous multiorgan transplants were protective (aHR 0.21 vs. LT only, 95% CI: 0.08-0.58, p <0.01). Development of acute rejection (both early and late) was independently associated with significantly reduced graft (aHR 3.13, 95% CI: 2.21-4.42, p <0.001) and patient survival (aHR 3.42, 95% CI: 2.35-4.98, p <0.001). In this 11-year Australian study, acute LT rejection occurred in 35%, with independent risk factors of younger recipient age and ABO-incompatible transplant, while having a simultaneous multiorgan transplant was protective. Acute rejection was independently associated with reduced graft and patient survival after adjustment for other factors.

Outcome of ABO-incompatible Live Donor Renal Transplant: Our Experience in Tertiary Care Center of Northwest India

Outcome of ABO-incompatible Live Donor Renal Transplant: Our Experience in Tertiary Care Center of Northwest India

(356) - ABO Genotype and its Relation on Histo-Blood Antigen Expression and Regeneration Following Removal - Potential Significance in ABO Incompatible Transplantation

(356) - ABO Genotype and its Relation on Histo-Blood Antigen Expression and Regeneration Following Removal - Potential Significance in ABO Incompatible Transplantation

(369) - A-Antigen Re-Expression and Prevention of Hyperacute Rejection Following In Vivo Enzymatic Treatment in a Model of ABO-Incompatible Transplantation

(369) - A-Antigen Re-Expression and Prevention of Hyperacute Rejection Following In Vivo Enzymatic Treatment in a Model of ABO-Incompatible Transplantation

Transfusion Support in Hematopoietic Stem Cell Transplantation: A Contemporary Narrative Review.

Hematopoietic stem cell transplantation (HSCT) is a cornerstone of modern medical practice, and can only be performed safely and effectively with appropriate transfusion medicine support. Patients undergoing HSCT often develop therapy-related cytopenia, necessitating differing blood product requirements in the pre-, peri-, and post-transplant periods. Moreover, ensuring optimal management for patients alloimmunized to human leukocyte antigens (HLA) and/or red blood cell (RBC) antigens, as well as for patients receiving ABO-incompatible transplants, requires close collaboration with transfusion medicine and blood bank professionals. Finally, as updated transfusion guidelines and novel blood product modifications emerge, the options available to the transplant practitioner continue to expand. Herein, we detail contemporary blood transfusion and transfusion medicine practices for patients undergoing HSCT.

Outcome of ABO-incompatible living-donor kidney transplants : Aplea for crossover living-donor kidney transplantation

The lack of postmortem donated organs is the background to varyingly high rates of living-donor kidney transplants worldwide. ABO blood group-incompatible living-donor kidney transplants have also been established for at least 20years. The equivalence of the results of ABO-incompatible and ABO-compatible transplants has recently been questioned. In the sense of acritical reflection of our own kidney transplant program, we were interested in comparing ABO-incompatible with ABO-compatible living-donor kidney transplants. Aretrospective analysis of the long-term outcomes of all living-donor kidney transplants performed at our center since the first ABO-incompatible transplants were performed in 2005 up to and including 2022 was performed. Between 2005 and 2022, 1099 living kidney transplants were performed at the authors' center. Among them were 241ABO-incompatible transplants. Transplant survival was significantly lower after ABO-incompatible donation than after ABO-compatible donation. This effect consisted of an increased mortality of the recipients, especially in the early phase, and areduced longevity of the grafts. Including ABO-incompatible pairs for living-donor kidney transplants in crossover programs can improve medical outcomes and reduce costs.

High-Dose Intravenous Immunoglobulin to Treat Anti-Thymocyte Globulin Induction–Related BK Virus and Cytomegalovirus Infection in Patients with ABO-Incompatible Kidney Transplantation

ABO-incompatible (ABOi) transplantation is a novel method transplantation method that carries a heightened risk of infection caused by the use of high immunosuppressant doses. This elevated risk is particularly concerning for viral infections, such as cytomegalovirus (CMV) and the BK virus (BKV) increases. Herein, we present a case where high-dose intravenous immunoglobulin (IVIG) was effective in treating viral infections after transplantation. A 41-year-old man underwent an ABOi transplantation. The initial isoagglutinin titer was 1:32. The patient received 200 mg of rituximab, and 3 rounds of plasmapheresis were performed. Subsequently, renal function remained normal; however, 7 months later, the renal function declined, and BK nephropathy and CMV infection were diagnosed through biopsy and serologic tests. The FK level was reduced, and mycophenolate mofetil was discontinued. Although ciprofloxacin and leflunomide were administered, their effects were minimal. Therefore, high-dose IVIG (1 g/kg) was administered 5 times over 5 weeks, which led to a reduction in BK viral load and CMV infectivity in the serum. High-dose IVIG may serve as a promising alternative treatment to mitigate early transplant rejection and BKV and CMV infections.

Incidence of postoperative cytomegalovirus and BK-polyoma virus infections and graft loss in ABO-incompatible renal transplant recipients: a multicenter retrospective study.

The current study aimed to examine the incidence of perioperative infections and graft viability in ABO-compatible and ABO-incompatible renal transplant recipients. We included 643 living donor renal transplant recipients registered in the Michinoku Renal Transplant Network from 1998 to 2021. Patients were divided into the ABO-compatible and ABO-incompatible kidney transplantation groups. We compared the characteristics of the two groups and evaluated the incidence of postoperative viral infections (cytomegalovirus and BK virus), graft loss-free survival, and overall survival between the two groups. Of 643 patients, 485 (75%) and 158 (25%) were ABO-compatible and ABO-incompatible renal transplant recipients, respectively. Postoperative viral infections, rituximab use, and plasma exchange were significantly more common in ABO-incompatible than in ABO-compatible transplant recipients. However, there were no significant differences in terms of other background characteristics. The ABO-incompatible group was more likely to develop viral infections than the ABO-compatible group. Graft loss-free survival and overall survival did not significantly differ between the two groups. According to the multivariate Cox regression analysis, ABO compatibility was not significantly associated with graft loss-free survival and overall survival. Although the incidence of postoperative viral infections in ABO-incompatible renal transplant recipients increased, there was no significant difference in terms of rejection events, graft loss-free survival, and overall survival.

Comparative Analysis of AB vs. ABO-specific Plasma for Desensitization in Blood Group O Recipients: An In Vitro Study.

Neutralizing capacity measurement (NCM) of soluble ABH substances (SAS) in plasma was assessed to guide the selection of the appropriate ABO group of fresh-frozen plasma (FFP) for plasma exchange (PE) in blood group O recipients with ABO-incompatible transplantations. Neutralizing capacity was assessed by measuring anti-A and/or anti-B titers in samples comprising one unit of O FFP and 10 O EDTA plasma samples and subtracting the binary logarithm of the titer in each group with a saline dilution. Ten EDTA plasma samples with Lewis b (Leb) antigen positivity and 10 sets of pooled FFP from each blood group were used as diluents. In O FFP, the NCM values (mean±SD) were 3.4±0.52 (2.6±0.52) and 2.6±0.52 (1.5±0.3) in B and AB for IgM (total antibody) anti-B (both P<0.001), and in the 10 O EDTA plasma samples, they were 3.9±0.88 (3.1±0.88) and 3.2±0.79 (2.4±0.97) for IgM (P=0.0013) and total anti-B (P=0.025), respectively. In vitro analysis revealed that B FFP is more effective than AB FFP in reducing IgM and total anti-B antibody titers in O recipients, regardless of Leb antigen positivity.

Clinical characteristics and risk factors for late-onset pneumocystis jirovecii pneumonia in kidney transplantation recipients.

Pneumocystis jirovecii pneumonia (PJP) is a common and troublesome complication of kidney transplantation. In the era of prophylaxis, the peak incidence of PJP after kidney transplantation and specific characteristics of late-onset PJP have always been debated. We performed a retrospective study by analysing the data of post-transplantation pneumonia in adult kidney transplantation recipients between March 2014 and December 2021 in The Affiliated First Hospital of University of Science and Technology of China (USTC). A total of 361 patients were included and divided into early-onset PJP, late-onset PJP and non-PJP groups. The characteristics of each group and related risk factors for the late-onset patients were investigated. Some patients developed PJP 9 months later with a second higher occurrence between month 10 and 15 after transplantation. Compared with non-PJP, ABO-incompatible and cytomegalovirus (CMV) viremia were significantly associated with late onset of PJP in multivariate analysis. The use of tacrolimus, CMV viremia, elevated CD8(+) T cell percent and hypoalbuminemia were risk factors for late PJP. Receiver operating characteristic curve analysis demonstrated that a combination of those factors could increase the sensitivity of prediction remarkably, with an area under the curve of 0.82, a sensitivity of 80% and a specificity of 83%. PJP could occur months after kidney transplantation. ABO-incompatible transplant recipients are at high risk of PJP. In the later stages of transplantation, CMV viremia, T lymphocyte subsets percentage and serum albumin levels should be monitored in patients using tacrolimus.

Association between the early high level of serum tacrolimus and recurrence of hepatocellular carcinoma in ABO-incompatible liver transplantation.

Clinical factors predicting graft survival (GS) after ABO-incompatible (ABOi) liver transplantation (LT), and differences between recipients with and without hepatocellular carcinoma (HCC) are unclear. To analyze the impact of serial serum tacrolimus trough concentration in recipients with or without HCC) in ABOi living-donor liver transplantation (LDLT). We analyzed a historical cohort of 89 recipients who underwent ABOi LDLT, including 47 patients with HCC. The 1-, 3-, 5-, and 10-year GS rates were 85.9%, 73.3%, 71.4%, and 71.4%, respectively, and there were no significant differences between HCC and non-HCC recipients. In multivariate Cox-regression analyses, tacrolimus trough concentrations below 5.4 ng/mL at 24 wk post-LT, in addition to the antibody-mediated rejection (AMR) were associated with poor-graft outcomes. In HCC patients, AMR [hazard ratio (HR) = 63.20, P < 0.01] and HCC recurrence (HR = 20.72, P = 0.01) were significantly associated with poor graft outcomes. HCCs outside Milan criteria, and tacrolimus concentrations at 4 wk post-LT > 7.3 ng/mL were significant predictive factors for HCC recurrence. After propensity score matching, patients with high tacrolimus concentrations at 4 wk had significantly poor recurrence-free survival. Elevated tacrolimus levels at 4 wk after ABOi LDLT have been found to correlate with HCC recurrence. Therefore, careful monitoring and control of tacrolimus levels are imperative in ABOi LT recipients with HCC.

Liver Transplantation for Zellweger Syndrome.

Zellweger syndrome or cerebrohepatorenal syndrome is a rare, multisystem disorder occurring due to defect in metabolic pathway within the peroxisomes. Cirrhosis with portal hypertension is an important presentation of these patients. Given its progressive, multisystem nature, the role of liver transplantation (LT) in Zellweger syndrome remains undefined and controversial. An 11-y-old boy diagnosed with Zellweger syndrome presented to theauthors with decompensated cirrhosis along with bilateral proptosis. After a meticulous evaluation, he was offered an ABO incompatible liver transplantation with hismother being the donor. He had an uneventful post operative period. After a follow up of 24 mo, he has normal graft function,normal cognition along with resolution of proptosis. Therefore, in a group of carefully selected patients with Zellweger syndrome, a liver transplantation can be offered successfully with an excellent prognosis.

I-JAMM-(I): A survey providing an insight into the practices of isoagglutinin titration in ABO incompatible kidney and liver transplantation

Background and objectivesABO-incompatible transplantations allow patients to receive timely transplants. Isoagglutinin titration to ascertain levels of incompatible antibodies in the recipient is important in determining patient selection and transplant survivability. To find out the prevalent trends in India, the largest, first of its kind survey was carried out among the transplant centers regarding their practices in isoagglutinin titration. MethodsThe survey was drafted by a working group of Transfusion and Transplant Immunology specialists from six different centers. Data was obtained via the use of an online questionnaire. ResultsResults were categorized into four categories, Hospital information, Titration methodology, Role of transfusion specialists and cut-off titers. Most centers had a well-established solid-organ transplant program with considerable number of ABO-incompatible transplantations. Most centers performed isoagglutinin titration in Transfusion Medicine department. Column Agglutination Technique (CAT) was the most common method, using EDTA blood samples and freshly-prepared in-house pooled cells. Most centers had a turn-around time of less than 12 h. While the policy for ascertaining baseline and threshold titers is well-defined in ABO-incompatible renal transplants, variations from center to center still exist for ABO-incompatible liver transplants. Most centers required a Transfusion Medicine consultation for the patients before such transplants. ConclusionWith increasing ABO-incompatible kidney and liver transplants across the country, the role of Transfusion medicine specialists has become vital in pre-conditioning regimes enabling the viability and success of such transplants. This was a unique survey that provided a snapshot of current trends and practices of isoagglutinin titration for ABO-incompatible transplants in India.

Conquering immunological barrier in kidney transplantation: ABO incompatible transplantation

No abstract available

Two Hit Theory for the Pathogenesis of Type 3 Congenital Amegakaryocytic Thrombocytopenia

Congenital amegakaryocytic thrombocytopenia (CAMT) is an autosomal recessive disorder characterized by thrombocytopenia with an absence of megakaryocytes. It can lead to aplastic anemia or myelodysplastic syndrome (MDS). CAMT is linked to a mutation in the c-MPL gene on chromosome 1, which encodes the thrombopoietin receptor. In 2005, CAMT was categorized into three types based on the severity of c-MPL gene loss. Type 1 is the most severe, leading to early-onset pancytopenia and bone marrow abnormalities. Type 2 shows a temporary increase in platelets during infancy, followed by bone marrow failure at 3-6 years due to partial gene function. Type 3 has normal c-MPL function but produces ineffective megakaryocytes. We report a case of a patient with CAMT-like symptoms, without a c-MPL gene mutation, suggesting the presence of an alternative genetic defect. Methods Multi-institutional collaboration and review of medical records in addition to PubMed search for thrombocytopenia, bleeding complications, macrocytosis, trisomy 6, GATA2 variant, inherited bone marrow failure. Case Description A 12-year-old male with severe thrombocytopenia initially observed at 2 years of age. Bleeding complications included scalp hematoma, excessive bleeding during adenoidectomy, widespread petechiae, purpura, epistaxis, and gum bleeding. During this time platelet count ranged between 30-80,000 x10 3/uL. At 10 years of age, bleeding worsened with platelet counts of 6-20,000 x10 3/uL. Mean platelet volume (MPV) remained within the normal range. Simultaneously there was a decline in hemoglobin and the emergence of macrocytosis. Mother had moderate thrombocytopenia during pregnancy, older sibling with similar thrombocytopenia but asymptomatic. Clinical presentation made immune thrombocytopenia, autoimmune disorders, and immune dysregulation-induced platelet destruction unlikely. Inherited thrombocytopenia panel testing for 42 germline variants was negative. Bone marrow biopsy showed 60% cellularity and was remarkable for a decrease in megakaryocytes. Cytogenetic analysis revealed trisomy 6 in 7/20 metaphases. Molecular hematopathology identified a GATA2 variant in 50% of the alleles. Inherited BMF panel revealed heterozygosity for multiple variants of unknown significance (VUS), including c.5096A&amp;gt;G (p.Asp1699Gly) in BRCA2 gene, c.3898A&amp;gt;G (p.Ile300Val) in LYST gene, 1408A&amp;gt;G (p.Thr470Ala) in PALB2 gene, and c.7240G&amp;gt;A (p.Val2414Met) in tVPS13B gene. Another BMF panel revealed two additional heterozygous VUS - NBEAL2 and ADAMTS13. Testing for Fanconi anemia and dyskeratosis congenita were negative. Whole exome sequencing revealed heterozygosity for a 1.57 Mb duplication on chromosome 3q29. Additional molecular pathology panel testing for 468 genes, germline genetic testing for lysosomal disorders and mucopolysaccharidoses, were also negative. Repeat bone marrow testing demonstrated a progressive decrease in cellularity to 5-30% with trilineage hypoplasia. With extensive yet inconclusive diagnostic workup, worsening clinical presentation, and progressive hypocellularity of the bone marrow, he underwent an ABO incompatible stem cell transplantation (9:10, A HR) from a mismatched unrelated donor. The conditioning regimen was myeloablative with busulfan, cyclophosphamide, anti-thymocyte globulin, and post-transplant cyclophosphamide. Currently, he is 150 days post-transplant with peripheral blood chimerism demonstrating 97.7% donor on day 98. Platelet counts have normalized, and he has not required a transfusion for nearly 100 days. Discussion This case report highlights the concept of a “double hit” hypothesis. While homozygous mutations of PALB2 and BRCA2 are individually associated with Fanconi anemia and BMF syndromes, no hematological pathology has been documented in their heterozygous forms, raising the question of whether the co-expression of these variants in a heterozygous state could result in a similar disease phenotype as their homozygous counterparts. This finding prompts further exploration into the potential impact of combined variants on disease manifestation.

Pathogenetic Subtypes of Pure Red Cell Aplasia and Therapeutic Management Strategies : A Single Centre Experience in the United Kingdom of 75 Patients over 10 Years

Introduction Pure red cell aplasia (PRCA) is a syndrome characterised by a severe anemia, reticulocytopenia and severe depletion of erythroid precursors in an otherwise unremarkable bone marrow. PRCA arises congenitally in Diamond-Blackfan Anemia and usually presents in childhood. Acquired PRCA can occur at any age, can be transient due to infections such as from parvovirus B19, or more chronic, secondary to autoimmune conditions, malignancies especially thymoma, erythropoiesis stimulating agents, , pregnancy and ABO incompatible hematopoetic stem cell transplantation. PRCA is also known to arise from drug and toxin exposure. Haematological malignancy/clonal disorders for e.g. CLL, MGUS, T-LGLs have well known associations with PRCA. PRCA can also be a feature of myelodysplastic syndrome and can herald evolution to aplastic anemia. Despite the heterogeneity in aetiology, the mainstay of treatment remains immunosuppression with steroids and/or ciclosporin. Here, we report our single centre experience of a large cohort of 75 patients with PRCA, referred to our centre over a 10 year period. Methods Patients with pure red cell aplasia referred to the Department of Hematological Medicine at King's College Hospital were identified by interrogation of the Electronic Patient Record (EPR) and pathology systems. The search terms used were a clinical or pathological diagnosis of ‘pure red cell aplasia’ or ‘PRCA’. Our hospital receives diagnostic samples from the South East of England, therefore data was collected only for patients with clinical information available. Patients (n=33) who developed PRCA post-allogeneic stem cell transplant were excluded. Results A total of 75 patients with both a pathological diagnosis of PRCA and available clinical information were identified, 31 (41.3%) were female. Median age was 51 years (range 9 - 84). The majority of patients had underlying conditions known to be associated with PRCA. Of the haematological conditions, PRCA was most seen in association with MDS (Table 1). Of the 75 patients in our cohort, 82% (61/75) required treatment for PRCA and 57% (43/75) required two or more lines of therapy. In total 25.3% (19/75) patients received corticosteroids as first line therapy. Of those, 75% showed a response, with 50% achieved a complete response. The response rate was less favourable (57%) in those patients in whom ciclosporin was used as first line therapy. Most common second line therapy was Ciclosporin (22.3%) followed by Cyclophosphamide (4%), Sirolimus (2.7%) and Anti-Thymocyte Globulin (1.33%). Of the cohort with an underlying MDS, 52% (11/21) responded to treatment, compared to 65% of those with idiopathic PRCA, likely reflective of the recalcitrant nature of PRCA in MDS. Other therapies received were IVIG, erythropoietin and disease-directed therapy,e.g lenalidomide for MDS with 5q- and thymectomy. Median follow of patients were 42 months.The overall survival of PRCA since last follow up was 50% for the cohort as a whole and 63% for those without an associated malignancy or clonal disorder. D iscussion In this large single centre experience of PRCA, we describe a lower incidence of idiopathic PRCA, lower median age despite a large proportion of MDS and increased incidence in male as compared to published literature. Response to initial therapy was seen in the majority of idiopathic PRCA patients, however response was lower in patients with an underlying malignancy. Of note we identified STAT3 mutations in two patients, highlighting the role of molecular testing and keeping a broad differential diagnosis when presented with this rare condition.