Different Neutralization Profiles After Primary SARS-CoV-2 Omicron BA.1 and BA.2 Infections.

Background and Methods: The SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) Omicron (B.1.1.529) variant is the antigenically most distinct variant to date. As the heavily mutated spike protein enables neutralization escape, we studied serum-neutralizing activities of naïve and vaccinated individuals after Omicron BA.1 or BA.2 sub-lineage infections in live virus neutralization tests with Omicron BA.1, Omicron BA.2, wildtype (WT, B1.1), and Delta (B.1.617.2) strains. Serum samples obtained after WT infections and three-dose mRNA vaccinations with and without prior infection were included as controls. Results: Primary BA.1 infections yielded reduced neutralizing antibody levels against WT, Delta, and Omicron BA.2, while samples from BA.2-infected individuals showed almost no cross-neutralization against the other variants. Serum neutralization of Omicron BA.1 and BA.2 variants was detectable after three-dose mRNA vaccinations, but with reduced titers. Vaccination-breakthrough infections with either Omicron BA.1 or BA.2, however, generated equal cross-neutralizing antibody levels against all SARS-CoV-2 variants tested. Conclusions: Our study demonstrates that although Omicron variants are able to enhance cross-neutralizing antibody levels in pre-immune individuals, primary infections with BA.1 or BA.2 induced mostly variant-specific neutralizing antibodies, emphasizing the differently shaped humoral immunity induced by the two Omicron variants. These data thus contribute substantially to the understanding of antibody responses induced by primary Omicron infections or multiple exposures to different SARS-CoV-2 variants and are of particular importance for developing vaccination strategies in the light of future emerging variants.

Heterogeneous SARS-CoV-2-Neutralizing Activities After Infection and Vaccination.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) with different resistance levels to existing immunity have recently emerged. Antibodies that recognize the SARS-CoV-2 spike (S) protein and exhibit neutralizing activities are considered the best correlate of protection and an understanding of humoral immunity is crucial for controlling the pandemic. We thus analyzed such antibodies in individuals recovered from infection in 2020 as well as vaccinees after two doses of an mRNA vaccine. Methods: Neutralizing antibody responses against three SARS-CoV-2 variants (D614G, VOCs Beta and Delta) were determined in serum samples from 54 infected individuals (24 non-hospitalized, 30 hospitalized) and 34 vaccinees shortly after symptom onset or second vaccination, respectively, as well as six months later. In addition, the effect of the S sequence of the infecting strain on neutralization was studied. Results: Non-hospitalized patients had the lowest neutralization titers against all variants, while those of hospitalized patients equaled or exceeded those of vaccinees. Neutralizing activity was lower against the two VOCs and declined significantly in all cohorts after six months. This decrease was more pronounced in hospitalized and vaccinated individuals than in non-hospitalized patients. Of note, the specific neutralizing activity (NT titer/ELISA value ratio) was higher in the infected cohorts than in vaccinees and did not differ between non-hospitalized and hospitalized patients. Patients infected with viral strains carrying mutations in the N-terminal domain of the spike protein were impaired in Beta VOC neutralization. Conclusions: Specific neutralizing activities were higher in infected than in vaccinated individuals, and no difference in the quality of these antibodies was observed between hospitalized and non-hospitalized patients, despite significantly lower titers in the latter group. Additionally, antibody responses of infected individuals showed greater heterogeneity than those of vaccinees, which was associated with mutations in the spike protein of the infecting strain. Overall, our findings yielded novel insights into SARS-CoV-2-specific neutralizing antibodies, evolving differently after virus infection and COVID-19 vaccination, which is an important issue to consider in ongoing vaccine strategy improvements.

Topical imiquimod compared with conization to treat cervical high-grade squamous intraepithelial lesions: Multicenter, randomized controlled trial.

OBJECTIVE: In a previous phase II trial, we showed that topical imiquimod (IMQ) therapy is an efficacious treatment for high-grade squamous intraepithelial lesion (HSIL). Aim of the present study was to investigate the non-inferiority of a 16-week topical, self-applied IMQ therapy compared to large loop excision of the transformation zone (LLETZ) in patients diagnosed with HSIL. METHODS: Phase III randomized, controlled, multicenter, open trial performed by Austrian Gynecologic Oncology group. Patients with histologically proven cervical intraepithelial neoplasia (CIN)2 (30 years and older) or CIN3 (18 years and older) and satisfactory colposcopy were randomized to topical IMQ treatment or LLETZ. Successful treatment was defined as negative HPV high-risk test result 6 months after start of the treatment. Secondary endpoints were histological outcome and HPV clearance rates. RESULTS: Within 3 years 93 patients were randomized, received the allocated treatment and were available for ITT analysis. In the IMQ group negative HPV test at 6 months after treatment start was observed in 22/51 (43.1%) of patients compared to 27/42 (64.3%) in the LLETZ group on ITT analysis (rate difference 21.2%-points, 95% two-sided CI: 0.8 to 39.1). In the IMQ group histologic regression 6 months after treatment was observed in 32/51 (63%) of patients and complete histologic remission was observed in 19/51 (37%) of patients. Complete surgical resection was observed in 84% after LLETZ. CONCLUSION: In women with HSIL, IMQ treatment results in lower HPV clearance rates when compared to LLETZ. LLETZ remains the standard for women with HSIL when treatment is required. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01283763, EudraCT number: 2012-004518-32.

SARS-CoV-2 mutations in MHC-I-restricted epitopes evade CD8+ T cell responses.

CD8+ T cell immunity to SARS-CoV-2 has been implicated in COVID-19 severity and virus control. Here, we identified nonsynonymous mutations in MHC-I-restricted CD8+ T cell epitopes after deep sequencing of 747 SARS-CoV-2 virus isolates. Mutant peptides exhibited diminished or abrogated MHC-I binding in a cell-free in vitro assay. Reduced MHC-I binding of mutant peptides was associated with decreased proliferation, IFN-γ production and cytotoxic activity of CD8+ T cells isolated from HLA-matched COVID-19 patients. Single cell RNA sequencing of ex vivo expanded, tetramer-sorted CD8+ T cells from COVID-19 patients further revealed qualitative differences in the transcriptional response to mutant peptides. Our findings highlight the capacity of SARS-CoV-2 to subvert CD8+ T cell surveillance through point mutations in MHC-I-restricted viral epitopes.

Clinical Relevance of Absolute BK Polyoma Viral Load Kinetics in Patients With Biopsy Proven BK Polyomavirus Associated Nephropathy.

Introduction: The absolute BK viral load is an important diagnostic surrogate for BK polyomavirus associated nephropathy (PyVAN) after renal transplant (KTX) and serial assessment of BK viremia is recommended. However, there is no data indicating which particular viral load change, i.e., absolute vs. relative viral load changes (copies/ml; percentage of the preceding viremia) is associated with worse renal graft outcomes. Materials and Methods: In this retrospective study of 91 biopsy proven PyVAN, we analyzed the interplay of exposure time, absolute and relative viral load kinetics, baseline risk, and treatment strategies as risk factors for graft loss after 2 years using a multivariable Poisson-model. Results: We compared two major treatment strategies: standardized immunosuppression (IS) reduction (n = 53) and leflunomide (n = 30). The median viral load at the index biopsy was 2.15E+04 copies/ml (interquartile range [IQR] 1.70E+03-1.77E+05) and median peak viremia was 3.6E+04 copies/ml (IQR 2.7E+03-3.3E+05). Treatment strategies and IS-levels were not related to graft loss. After correction for baseline viral load and estimated glomerular filtration rate (eGFR), absolute viral load decrease/unit remained an independent risk factor for graft loss [incidence rate ratios [IRR] = 0.77, (95% CI 0.61-0.96), p = 0.02]. Conclusion: This study provides evidence for the prognostic importance of absolute BK viremia kinetics as a dynamic parameter indicating short-term graft survival independently of other established risk factors.

CD4 T Cell Determinants in West Nile Virus Disease and Asymptomatic Infection.

West Nile (WN) virus infection of humans is frequently asymptomatic, but can also lead to WN fever or neuroinvasive disease. CD4 T cells and B cells are critical in the defense against WN virus, and neutralizing antibodies, which are directed against the viral glycoprotein E, are an accepted correlate of protection. For the efficient production of these antibodies, B cells interact directly with CD4 helper T cells that recognize peptides from E or the two other structural proteins (capsid-C and membrane-prM/M) of the virus. However, the specific protein sites yielding such helper epitopes remain unknown. Here, we explored the CD4 T cell response in humans after WN virus infection using a comprehensive library of overlapping peptides covering all three structural proteins. By measuring T cell responses in 29 individuals with either WN virus disease or asymptomatic infection, we showed that CD4 T cells focus on peptides in specific structural elements of C and at the exposed surface of the pre- and postfusion forms of the E protein. Our data indicate that these immunodominant epitopes are recognized in the context of multiple different HLA molecules. Furthermore, we observed that immunodominant antigen regions are structurally conserved and similarly targeted in other mosquito-borne flaviviruses, including dengue, yellow fever, and Zika viruses. Together, these findings indicate a strong impact of virion protein structure on epitope selection and antigenicity, which is an important issue to consider in future vaccine design.

Impact of flavivirus vaccine-induced immunity on primary Zika virus antibody response in humans.

BACKGROUND: Zika virus has recently spread to South- and Central America, causing congenital birth defects and neurological complications. Many people at risk are flavivirus pre-immune due to prior infections with other flaviviruses (e.g. dengue virus) or flavivirus vaccinations. Since pre-existing cross-reactive immunity can potentially modulate antibody responses to Zika virus infection and may affect the outcome of disease, we analyzed fine-specificity as well as virus-neutralizing and infection-enhancing activities of antibodies induced by a primary Zika virus infection in flavivirus-naïve as well as yellow fever- and/or tick-borne encephalitis-vaccinated individuals. METHODOLOGY: Antibodies in sera from convalescent Zika patients with and without vaccine-induced immunity were assessed by ELISA with respect to Zika virus-specificity and flavivirus cross-reactivity. Functional analyses included virus neutralization and infection-enhancement. The contribution of IgM and cross-reactive antibodies to these properties was determined by depletion experiments. PRINCIPAL FINDINGS: Pre-existing flavivirus immunity had a strong influence on the antibody response in primary Zika virus infections, resulting in higher titers of broadly flavivirus cross-reactive antibodies and slightly lower levels of Zika virus-specific IgM. Antibody-dependent enhancement (ADE) of Zika virus was mediated by sub-neutralizing concentrations of specific IgG but not by cross-reactive antibodies. This effect was potently counteracted by the presence of neutralizing IgM. Broadly cross-reactive antibodies were able to both neutralize and enhance infection of dengue virus but not Zika virus, indicating a different exposure of conserved sequence elements in the two viruses. CONCLUSIONS: Our data point to an important role of flavivirus-specific IgM during the transient early stages of infection, by contributing substantially to neutralization and by counteracting ADE. In addition, our results highlight structural differences between strains of Zika and dengue viruses that are used for analyzing infection-enhancement by cross-reactive antibodies. These findings underscore the possible impact of specific antibody patterns on flavivirus disease and vaccination efficacy.

Longitudinal assessment of the CXCL10 blood and urine concentration in kidney transplant recipients with BK polyomavirus replication-a retrospective study.

In kidney transplant recipients (KTRs), BK polyomavirus (BKPyV) replication may progress to polyomavirus-associated nephropathy (PVAN). In this retrospective study, we assessed the chemokine CXCL10 in urine and blood samples consecutively acquired from 85 KTRs who displayed different stages of BKPyV replication and eventually developed PVAN. In parallel to progression toward PVAN, CXCL10 gradually increased in blood and urine, from baseline (prior to virus replication) to BKPyV DNAuria (median increase in blood: 42.15 pg/ml, P = 0.0156), from mere DNAuria to low- and high-level BKPyV DNAemia (median increase: 52.60 and 87.26 pg/ml, P = 0.0010 and P = 0.0002, respectively) and peaked with histologically confirmed PVAN (median increase: 145.00 pg/ml, P < 0.0001). CXCL10 blood and urine levels significantly differed among KTRs with respect to simultaneous presence of human cytomegalovirus (P < 0.001) as well as in relation to the clinical severity of respective BKPyV DNAemia episodes (P = 0.0195). CXCL-10 concentrations were particularly lower in KTRs in whom BKPyV DNAemia remained without clinical evidence for PVAN, as compared to individuals who displayed high decoy cell levels, decreased renal function and/or biopsy-proven PVAN (median blood concentration: 266.97 vs. 426.42 pg/ml, P = 0.0282). In conclusion, in KTRs CXCL10 rises in parallel to BKPyV replication and correlates with the gradual development of PVAN.

Next-generation sequencing shows marked rearrangements of BK polyomavirus that favor but are not required for polyomavirus-associated nephropathy.

BACKGROUND: BKPyV is associated with polyomavirus-associated nephropathy (PVAN), a major cause of graft rejection in kidney transplant recipients (KTRs). Mutations occur in the transcriptional control region (TCR) of BKPyV, but whether they are required for the development of PVAN is not completely understood. To this end, we characterized BKPyV TCRs from KTRs to assess whether TCR mutations are associated with PVAN. STUDY DESIGN: We analyzed urine and plasma samples of fifteen KTRs with biopsy-confirmed PVAN, presumptive PVAN, or probable PVAN in order to explore the contents of the BKPyV virome. BKPyV TCRs were amplified and deep sequenced to characterize the viral strains. Alterations in block structures and transcription factor binding sites were investigated. RESULTS: The majority of sequences in both urine and plasma samples represented archetype BKPyV TCR. Minor populations harboring rearranged TCRs were detected in all patient groups. In one biopsy-confirmed PVAN patient rearranged TCRs predominated, and in another patient half of all reads represented rearranged sequences. CONCLUSIONS: Although archetype BKPyV predominated in most patients, highest proportions and highest numbers of rearranged strains were detected in association with PVAN. TCR mutations seem not necessary for the development of PVAN, but immunosuppression may allow increased viral replication giving rise to TCR variants with enhanced replication efficiency.

Multiplex analysis of Human Polyomavirus diversity in kidney transplant recipients with BK virus replication.

BACKGROUND: While the pathogenicity of the two initially identified Human Polyomaviruses (HPyVs), BK Virus (BKPyV) and JC Virus (JCPyV) has been intensely studied, there is only limited data, on whether the occurrence of the recently discovered HPyVs correlates with high level BKPyV replication and progression towards Polyomavirus associated nephropathy (PVAN). METHODS: Therefore, we performed a comprehensive longitudinal genoprevalence analysis of 13 HPyVs using a novel multiplex assay including 400 serum and 388 urine samples obtained from 99 kidney transplant recipients (KTRs), grouped by quantitative BKPyV DNA loads and evidence of manifest BKPyV associated disease (histologically verified PVAN, high urinary decoy cell levels and concurrent decrease of renal function). RESULTS: In total, 3 different non-BKPyV/JCPyV HPyVs, Human Polyomavirus 9, Merkel Cell Polyomavirus (MCPyV) and Trichodysplasia Spinulosa associated Polyomavirus were detected in 11 blood and 21 urine samples from 21 patients. Although DNAemia of these viruses occurred more frequently during high level BKPyV DNAemia and PVAN, the increase of the detection frequency due to progression of BKPyV replication did not reach statistical significance for blood samples. The positive detection rate of MCPyV in urine, however, was significantly higher during BKPyV DNAemia in 19 KTRs of our cohort who suffered from histologically verified PVAN (p = 0.005). In one individual with PVAN, continuous long-term shedding of MCPyV in urine was observed. CONCLUSION: In our cohort the recently discovered HPyVs HPyV9, TSPyV and MCPyV emerged in blood from KTRs with variable kinetics, while detection of MCPyV DNAuria occurred more frequently during BKPyV DNAemia in patients with PVAN.

Enterovirus infections in pediatric hematologic/oncologic patients.

BACKGROUND: Enteroviruses (EV) are a large group of Picornaviruses associated with respiratory, gastrointestinal, and neurologic symptoms in the immunocompetent host. Little is known about the epidemiologic and clinical impact in pediatric hematologic/oncologic patients. PROCEDURE: From 2001 through 2017, different clinical specimens were collected from pediatric hematologic/oncologic patients and were tested for enteroviral RNA. RESULTS: Of 13 004 specimens collected from 761 patients, 38 (0.3%) obtained from 14 patients (1.8%) tested positive for EV RNA. Viral shedding was observed without viremia and vice versa. None of 80 cerebrospinal fluid specimens obtained from 60 patients with neurologic symptoms were positive for EV RNA. None of 14 patients positive for EV RNA showed EV-specific symptoms. In 11/14 patients, EV RNA was found to be negative in the follow-up specimen. The remaining patient with a severe primary immune deficiency showed repeated positive EV RNA results for >5 years. CONCLUSIONS: In this pediatric hematologic/oncologic cohort, EV infection occurred rarely and without related symptoms. Specimens concurrently obtained from one patient are commonly not in accordance with each other. In the vast majority of patients, EV RNA appears to turn negative in the follow-up specimen. EV infections seem to have a low impact in this patient cohort.

Structural Influence on the Dominance of Virus-Specific CD4 T Cell Epitopes in Zika Virus Infection.

Zika virus (ZIKV) has recently caused explosive outbreaks in Pacific islands, South- and Central America. Like with other flaviviruses, protective immunity is strongly dependent on potently neutralizing antibodies (Abs) directed against the viral envelope protein E. Such Ab formation is promoted by CD4 T cells through direct interaction with B cells that present epitopes derived from E or other structural proteins of the virus. Here, we examined the extent and epitope dominance of CD4 T cell responses to capsid (C) and envelope proteins in Zika patients. All patients developed ZIKV-specific CD4 T cell responses, with substantial contributions of C and E. In both proteins, immunodominant epitopes clustered at sites that are structurally conserved among flaviviruses but have highly variable sequences, suggesting a strong impact of protein structural features on immunodominant CD4 T cell responses. Our data are particularly relevant for designing flavivirus vaccines and their evaluation in T cell assays and provide insights into the importance of viral protein structure for epitope selection and antigenicity.

Malignancy and chemotherapy induced haemophagocytic lymphohistiocytosis in children and adolescents-a single centre experience of 20 years.

Haemophagocytic lymphohistiocytosis (HLH) is a possibly life-threatening syndrome of immune dysregulation and can be divided into primary (hereditary) and secondary forms (including malignancy-associated HLH (M-HLH)). We retrospectively analysed epidemiological, clinical, virological and laboratory data from patients with M-HLH treated at our department between 1995 and 2014. Out of 1.706 haemato-/oncologic patients treated at our department between 1995 and 2014, we identified 22 (1.29%) patients with secondary HLH (1.3-18.0, median 10.1 years; malignancy induced n = 2; chemotherapy induced n = 20). Patients with acute myeloblastic leukaemia (AML) developed HLH significantly more often than patients with acute lymphoblastic leukaemia (ALL) (10/55, 18.2% vs. 6/148, 4.1%, p = 0.0021). As possible viral triggers, we detected BKV (53.8% of the tested patients), HHV-6 (33.3%), EBV (27.8%), CMV (23.5%), ADV (16.7%) and PVB19 (16.7%) significantly more frequently than in haemato-/oncologic patients without HLH. Despite lacking evidence of concurrent bacterial infection, C-reactive protein (CRP) and procalcitotnin (PCT) were elevated in 94.7 and 77.7% of the patients, respectively. Ferritin and sIL2R were markedly elevated in all patients. HLH-associated mortality significantly (p = 0.0276) decreased from 66.6% (1995-2004) to 6.25% (2005-2014), suggesting improved diagnostic and therapeutic management. Awareness of HLH is important, and fever refractory to antibiotics should prompt to consider this diagnosis. Elevated ferritin and sIL2R seem to be good markers, while inflammatory markers like CRP and PCT are not useful to discriminate viral triggered HLH from severe bacterial infection. Re-/activation of several viruses may play a role as possible trigger.

Activation of the ileal neuroendocrine tumor cell line P-STS by acetylcholine is amplified by histamine: role of H3R and H4R.

Neuroendocrine tumors may present with pseudoallergic reactions like diarrhea and idiopathic anaphylaxis. Here we present the P-STS human ileal neuroendocrine cell line as a model cell line for these tumors. Neuroendocrine markers and changes in cytoplasmic calcium concentration ([Ca2+]i) in response to several possible activators of 5-hydroxytryptamine (5-HT) release were analyzed. P-STS cells still expressed chromogranin A and synaptophysin after 2 years of culture. Tryptophan hydroxylase 1 mRNA and a low amount of 5-HT were also detected. Acetylcholine (ACh) caused a rise in [Ca2+]i. Somatostatin inhibited, whereas histamine (HA) but not the HA receptor ligand betahistine enhanced activation by ACh. The [Ca2+]i response to ACh/HA was inhibited by the HA receptor H3 (H3R) agonist methimepip and by the antidepressant imipramine. Further [Ca2+]i response studies indicated the presence of H4Rs and of a functional calcium sensing receptor. High or low affinity IgE receptor protein or mRNA were not detected. Taken together, neuroendocrine markers and response to intestinal neurotransmitters approve the P-STS cell line as a valuable model for enterochromaffin cells. Enhancement of their ACh-induced pro-secretory response by HA, with a role for H3R and H4R, suggests an amplifying role of neuroendocrine cells in allergen-induced diarrhea or anaphylaxis.

Evaluation of a multiplex ligation-dependent probe amplification assay for the detection of respiratory pathogens in oncological patients.

BACKGROUND: Respiratory tract infections are widespread and may cause significant morbidity and mortality in immunosuppressed populations such as oncological patients. OBJECTIVES: The RealAccurate Respiratory RT PCR Kit covering 14 respiratory viruses was compared to the RespiFinder Smart22, a broad-spectrum multiplex ligation-dependent probe amplification (MLPA) test, targeting 22 viral and bacterial respiratory pathogens. STUDY DESIGN: After verification of its analytical performance, the clinical performance of the RespiFinder Smart22 was evaluated by re-analysis of 96 respiratory samples from oncological patients. Additionally, the time to result (TTR) of both methods was compared. RESULTS: The analytical performance of the RespiFinder Smart22 fulfilled all previously specified criteria. Concordant results in both assays were achieved in 74.0% of all clinical specimens and in 91.2% when only positive results were taken into account. The RespiFinder Smart22 yielded additional results in a total of 22 (22.9% of 96) samples due to higher test sensitivity and a broader, highly multiplexed spectrum of pathogens. The TTR of a typical routine test consisting of three samples were 206 and 356 min for the RealAccurate Respiratory RT PCR Kit and the RespiFinder Smart22, respectively. However, hands-on time was reduced by 59.0% applying the MLPA method. CONCLUSIONS: In our hands, the RespiFinder Smart22 showed excellent analytical performance while hands-on time was halved in comparison to the RT PCR method. Regarding the clinical evaluation, the MLPA method provided additional results in 22.9% (22/96) of specimens due to its comprehensive format, higher test sensitivity and the capability to detect 22 pathogens compared to 14 with the RealAccurate Respiratory RT PCR Kit.

High detection rate of Trichomonas vaginalis in benign hyperplastic prostatic tissue.

While Trichomonas vaginalis, a protozoan parasite, is a well-investigated pathogen in the female population, there is little awareness of its significance in the male uro-genital tract. The presence of T. vaginalis in the prostate gland has only been scarcely investigated and has never been attested in conditions other than clinical prostatitis. Still, by some authors, this organ is regarded as ecologic niche for T. vaginalis. Since normal prostate tissue of sufficient quality is hard to come by, we investigated samples from 86 patients (mean age 68.7 ± 7.6 years) suffering from benign prostatic hyperplasia (BPH), a medical condition currently ranked as noninfectious, but characterized by chronic inflammatory tissue infiltrates of unknown etiology. Applying two different PCR protocols and sequence analysis of the respective amplicons, we detected T. vaginalis DNA in 29/86 (34%) BPH tissue samples, whereas in only 2/86 (2.3%) cases T. vaginalis grew in culture. Detection of T. vaginalis DNA correlated significantly (P < 0.01) with elevated peripheral blood monocytic cell counts, appearing along with protozoan infections. Given the unexpected high prevalence of T. vaginalis in BPH tissue of a nonselected, elderly study population from Austria, further epidemiological studies have to confirm this finding. Potential interactions of T. vaginalis in its prostatic habitat may be investigated with respect to their possible contribution to the inflammatory pathogenesis of BPH, since inflammatory cytokines have been shown to sustain prostatic hyperplastic growth.

The spectrum of parvovirus b19 infection in a pediatric hemato-oncologic ward.

Of 1059 children, 35 children with various hemato-oncologic diseases were diagnosed with parvovirus B19 infection. The clinical spectrum included 11 immunocompromised patients presenting with prolonged pancytopenia, 7 patients with delayed hematologic recovery after stem cell transplantation, 5 patients with parvovirus B19 as possible cause of severe aplastic anemia or myelodysplastic syndrome, and 12 children with hemolytic anemia and transient aplastic crisis.