CRISPR-Cas9 Editing of the HBG1 and HBG2 Promoters to Treat Sickle Cell Disease.

BACKGROUND: Sickle cell disease is caused by a defect in the ß-globin subunit of adult hemoglobin. Sickle hemoglobin polymerizes under hypoxic conditions, producing deformed red cells that hemolyze and cause vaso-occlusion that results in progressive organ damage and early death. Elevated fetal hemoglobin levels in red cells protect against complications of sickle cell disease. OTQ923, a clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9-edited CD34+ hematopoietic stem- and progenitor-cell (HSPC) product, has a targeted disruption of the HBG1 and HBG2 (γ-globin) gene promoters that increases fetal hemoglobin expression in red-cell progeny. METHODS: We performed a tiling CRISPR-Cas9 screen of the HBG1 and HBG2 promoters by electroporating CD34+ cells obtained from healthy donors with Cas9 complexed with one of 72 guide RNAs, and we assessed the fraction of fetal hemoglobin-immunostaining erythroblasts (F cells) in erythroid-differentiated progeny. The gRNA resulting in the highest level of F cells (gRNA-68) was selected for clinical development. We enrolled participants with severe sickle cell disease in a multicenter, phase 1-2 clinical study to assess the safety and adverse-effect profile of OTQ923. RESULTS: In preclinical experiments, CD34+ HSPCs (obtained from healthy donors and persons with sickle cell disease) edited with CRISPR-Cas9 and gRNA-68 had sustained on-target editing with no off-target mutations and produced high levels of fetal hemoglobin after in vitro differentiation or xenotransplantation into immunodeficient mice. In the study, three participants received autologous OTQ923 after myeloablative conditioning and were followed for 6 to 18 months. At the end of the follow-up period, all the participants had engraftment and stable induction of fetal hemoglobin (fetal hemoglobin as a percentage of total hemoglobin, 19.0 to 26.8%), with fetal hemoglobin broadly distributed in red cells (F cells as a percentage of red cells, 69.7 to 87.8%). Manifestations of sickle cell disease decreased during the follow-up period. CONCLUSIONS: CRISPR-Cas9 disruption of the HBG1 and HBG2 gene promoters was an effective strategy for induction of fetal hemoglobin. Infusion of autologous OTQ923 into three participants with severe sickle cell disease resulted in sustained induction of red-cell fetal hemoglobin and clinical improvement in disease severity. (Funded by Novartis Pharmaceuticals; ClinicalTrials.gov number, NCT04443907.).

Autochthonous Dengue Fever in 2 Patients, Rome, Italy.

Since August 2023, outbreaks of dengue virus (DENV) infection have occurred in Italy. We report 2 autochthonous case-patients and their extended follow-up. Despite persistent DENV detected in blood by PCR, results for antigenomic DENV RNA were negative after day 5, suggesting that a 5-day isolation period is adequate to avoid secondary cases.

A case of severe Plasmodium ovale malaria with acute respiratory distress syndrome and splenic infarction in a male traveller presenting in Italy.

BACKGROUND: Plasmodium ovale malaria is usually considered a tropical infectious disease associated with low morbidity and mortality. However, severe disease and death have previously been reported. CASE PRESENTATION: A case of severe P. ovale malaria in a healthy Caucasian man with a triangle splenic infarction and clinical progression towards Acute Respiratory Distress Syndrome was reported despite a rapid response to oral chloroquine treatment with 24-h parasitaemia clearance. CONCLUSION: Plasmodium ovale malaria is generally considered as a benign disease, with low parasitaemia. However, severe disease and death have occasionally been reported. It is important to be aware that occasionally it can progress to serious illness and death even in immunocompetent individuals.

A machine learning approach for early identification of patients with severe imported malaria.

BACKGROUND: The aim of this study is to design ad hoc malaria learning (ML) approaches to predict clinical outcome in all patients with imported malaria and, therefore, to identify the best clinical setting. METHODS: This is a single-centre cross-sectional study, patients with confirmed malaria, consecutively hospitalized to the Lazzaro Spallanzani National Institute for Infectious Diseases, Rome, Italy from January 2007 to December 2020, were recruited. Different ML approaches were used to perform the analysis of this dataset: support vector machines, random forests, feature selection approaches and clustering analysis. RESULTS: A total of 259 patients with malaria were enrolled, 89.5% patients were male with a median age of 39 y/o. In 78.3% cases, Plasmodium falciparum was found. The patients were classified as severe malaria in 111 cases. From ML analyses, four parameters, AST, platelet count, total bilirubin and parasitaemia, are associated to a negative outcome. Interestingly, two of them, aminotransferase and platelet are not included in the current list of World Health Organization (WHO) criteria for defining severe malaria. CONCLUSION: In conclusion, the application of ML algorithms as a decision support tool could enable the clinicians to predict the clinical outcome of patients with malaria and consequently to optimize and personalize clinical allocation and treatment.

Steroid use in measles: A retrospective cohort study during the 2017 outbreak in tertiary referral center, Rome and Latina, Italy.

INTRODUCTION: Since early January 2017, a new measles outbreak in Italy has been observed. The aim of the study was to compare features between adults and children measles cases and evaluate the effect of steroid treatment on the above parameters. METHODS: A retrospective multicenter, descriptive study was performed. We analyzed all patients admitted to the Department of Public Health and Infectious Diseases, Sapienza University, Rome and Latina, from January 2017 to December 2017 and discharged with diagnosis of measles. RESULTS: We identified 113 patients discharged with the diagnosis of measles infection cases of which 59 adults and 54 children (≤16 years). In adult population 32 patients (54 %) were males, with a median age of 30.5 years old and all unvaccinated (100 %). Keratoconjunctivitis 30 (50 %) was the most frequent complication. In pediatric population 27 (50 %) patients were males, with a median age of 3 years old. Information on measles vaccination status was available for only 21 (38.8 %) of cases. Keratoconjunctivitis 40 (74 %) was the most frequent complication. Analyzing the differences between adult and pediatric patients we found that children were significantly more likely to have keratoconjunctivitis and diarrhea as complications than adults in which the rate of thrombocytopenia and hepatitis was highest. Thirty-nine adult subjects (66 %) have been treated with systemic corticosteroids. CONCLUSIONS: Pediatric patients differ from adults in complications and liver involvement. Regarding steroids use, although there is no clear indication of steroid use during measles, there is no evidence of a worse outcome in our cases series.

Viral load decrease in SARS-CoV-2 BA.1 and BA.2 Omicron sublineages infection after treatment with monoclonal antibodies and direct antiviral agents.

The efficacy on the Omicron variant of the approved early coronavirus disease-2019 (COVID-19) therapies, especially monoclonal antibodies, has been challenged by in vitro neutralization data, while data on in vivo antiviral activity are lacking. We assessed potential decrease from Day 1 to Day 7 viral load (VL) in nasopharyngeal swabs of outpatients receiving Sotrovimab, Molnupiravir, Remdesivir, or Nirmatrelvir/ritonavir for mild-to-moderate COVID-19 due to sublineages BA.1 or BA.2, and average treatment effect by weighted marginal linear regression models. A total of 521 patients (378 BA.1 [73%], 143 [27%] BA.2) received treatments (Sotrovimab 202, Molnupiravir 117, Nirmatrelvir/ritonavir 84, and Remdesivir 118): median age 66 years, 90% vaccinated, median time from symptoms onset 3 days. Day 1 mean VL was 4.12 log2 (4.16 for BA.1 and 4.01 for BA.2). The adjusted analysis showed that Nirmatrelvir/ritonavir significantly reduced VL compared to all the other drugs, except versus Molnupiravir in BA.2. Molnupiravir was superior to Remdesivir in both BA.1 and BA.2, and to Sotrovimab in BA.2. Sotrovimab had better activity than Remdesivir only against BA.1. Nirmatrelvir/ritonavir showed the greatest antiviral activity against Omicron variant, comparable to Molnupiravir only in the BA.2 subgroup. VL decrease could be a valuable surrogate of drug activity in the context of the high prevalence of vaccinated people and low probability of hospital admission.

Effect of tecovirimat on healing time and viral clearance by emulation of a target trial in patients hospitalized for mpox.

Tecovirimat is a treatment option for severe mpox, although randomized clinical trials are ongoing. The aim of the study is to assess the effect of tecovirimat on healing time and the extent of viral clearance by target trial emulation using observational data. Clinical and virological data of patients hospitalized for mpox were collected. Samples from the upper respiratory tract (URT) were grouped in two time points: T1 (median 6 days from symptoms onset) and T2 (median 5 days from T1). Patients were followed-up until recovery. Average treatment effect (ATE) in patients untreated versus treated with tecovirimat was estimated on time to healing and variation in viral load in URT, using a weighted and cloning analysis. Among the 41 patients included, 19 completed a course of tecovirimat. The median time from symptoms onset to hospitalization and to drug-starting was 4 days and 10 days, respectively. No improvement in healing time in treated versus untreated was observed. No difference by treatment group in time to viral clearance was detected by ATE fitted in a subset of 13 patients after controlling for confounders. We found no evidence for a large effect of tecovirimat in shortening healing time and viral clearance. While awaiting the results of randomized studies, the use of tecovirimat should be restricted to the clinical trial setting.

Dual combined antiviral treatment with remdesivir and nirmatrelvir/ritonavir in patients with impaired humoral immunity and persistent SARS-CoV-2 infection.

Despite global vaccination efforts, immunocompromized patients remain at high risk for COVID-19-associated morbidity. In particular, patients with impaired humoral immunity have shown a high risk of persistent infection. We report a case series of adult patients with B cell malignancies and/or undergoing B cell targeting therapies with persisting SARS-CoV-2 infection and treated with a combination antiviral therapy of remdesivir and nirmatrelvir/ritonavir, in three Italian tertiary academic hospitals. A total of 14 patients with impaired adaptive humoral immunity and prolonged SARS-CoV-2 infection were treated with the dual antiviral therapy. The median age was 60 (IQR 56-68) years, and 11 were male. Twelve patients had B cell lymphoma, one patient had chronic lymphocytic leukemia and one patient had multiple sclerosis. Thirteen out of 14 patients had received prior B cell-targeting therapies, consisting of anti-CD20 monoclonal antibodies in 11 patients, and chimeric antigen receptor T therapy in 2 patients. The median time between diagnosis and therapy start was 42.0 (IQR 35-46) days. Seven patients had mild, 6 moderate and one severe disease. Nine patients had signs of interstitial pneumonitis on chest computed tomography scans before treatment. The median duration of nirmatrelvir/ritonavir and remdesivir combination therapy was 10 days. All patients showed resolution of COVID-19-related symptoms after a median of 6 (IQR 4-11) days and viral clearance after 9 (IQR 5-11) days. Combination therapy with remdesivir and nirmatrelvir/ritonavir is a promising treatment option for persistent COVID-19 in immunocompromized patients with humoral immunity impairment, worthy of prospective comparative trials.

The unmet need for COVID-19 treatment in immunocompromised patients.

BACKGROUND: Immunocompromised (IC) patients are at increased risk of severe and/or prolonged COVID-19. MAIN TEXT: The recent study by Scaglione et al., addresses the issue of IC outpatients with SARS-CoV-2 infection. Authors describe the real-life use of SARS-CoV-2 antivirals and/or monoclonal antibodies and the clinical benefit in high-risk COVID-19 patients. The study supports the use of early combination therapy in a subgroup of extremely high risk patients, and considers the combined strategy as a gold standard regimen to both increase the effectiveness of early treatment, especially in IC individuals, and, reduce the emergence of SARS-CoV-2 escape mutants. CONCLUSION: A tailored and standardised therapeutic approach in case of IC out and inpatients with SARS-CoV-2 infection is needed.

Epidemiological, clinical and virological characteristics of four cases of monkeypox support transmission through sexual contact, Italy, May 2022.

Since May 2022, an outbreak of monkeypox has been ongoing in non-endemic countries. We report four cases in Italy in young adult men reporting condomless sexual intercourse. The patients are in good clinical condition with no need for specific antiviral drugs. Biological samples from seminal fluid were positive for monkeypox viral DNA. For many other viruses found in semen there is no evidence of sexual transmission. The possibility of sexual transmission of monkeypox virus needs to be investigated.

Longitudinal Assessment of Multiple Immunological and Inflammatory Parameters during Successful DAA Therapy in HCV Monoinfected and HIV/HCV Coinfected Subjects.

In the direct-acting antiviral (DAA) era, it is important to understand the immunological changes after HCV eradication in HCV monoinfected (mHCV) and in HIV/HCV coinfected (HIV/HCV) patients. In this study, we analyzed sub-populations of monocytes, dendritic cells (DCs), T-lymphocytes and inflammatory biomarkers following initiation of DAA in 15 mHCV and 16 HIV/HCV patients on effective antiretroviral therapy at baseline and after sustained virological response at 12 weeks (SVR12). Fifteen age- and sex-matched healthy donors (HD) were enrolled as a control group. Activated CD4+ and CD8+ T-lymphocytes, mDCs, pDCs, MDC8 and classical, non-classical and intermediate monocytes were detected using flow cytometry. IP-10, sCD163 and sCD14 were assessed by ELISA while matrix metalloproteinase-2 (MMP-2) was measured by zymography. At baseline, increased levels of IP-10, sCD163 and MMP-2 were found in both HIV/HCV and mHCV patients compared to HD, whereas sCD14 increased only in HIV/HCV patients. After therapy, IP-10, sCD163 and sCD14 decreased, whereas MMP-2 persistently elevated. At baseline, activated CD8+ T-cells were high in HIV/HCV and mHCV patients compared to HD, with a decrease at SVR12 only in HIV/HCV patients. Activated CD4+ T-cells were higher in HIV/HCV patients without modification after DAAs therapy. These results suggest complex interactions between both viruses and the immune system, which are only partially reversed by DAA treatment.

Telemedicine During COVID-19 Pandemic: Lesson Learned from the Lazio Region Infectious Diseases and Emergency Department Network.

Telemedicine and teleconsultation can be powerful and useful tools for patients to hamper the physical barriers to access to health care services during COVID-19 pandemic. We describe the teleconsultation (TC) model in the Lazio Region. It uses a hub-and-spoke network system on geographic regional basis using a web based digital platform, termed ADVICE with the aim to connect regional Emergency Departments (EDs) and Infectious Diseases (ID) acute and critical care settings for patients with acute ID syndrome. Between January 2020 and June 2021, the ADVICE platform received 18.686 TCs: of them, 10838 requests (58%) were for ID TCs in 7996 patients, followed by 2555(13%) requests for trauma, 2286(12%) for acute complex syndrome and 1681 (8%) for Stroke TCs. Three quarter of ID TCs were requested for SARS-COV-2 infection, followed by sepsis management in 7% and tuberculosis in 6%. In 5416 TCs, 68%, diagnostic investigations and therapeutic prescriptions were recommended before admission, in 1941 TCs, 24%, the recommendation was patient admission and in 608 TCs, 7%, was to discharge patient at home. Telemedicine have ensured high-profile consultations for ID patients and during COVID-19 the use of this resource optimized clinical patient management.

The gp130 Cytokine Interleukin-11 Regulates Engraftment of Vav1-/- Hematopoietic Stem and Progenitor Cells in Lethally Irradiated Recipients.

During bone marrow transplantation, hematopoietic stem and progenitor cells (HSPCs) respond to signals from the hematopoietic microenvironment by coordinately activating molecular pathways through Rho GTPases, including Rac. We have previously shown that deletion of Vav1, a hematopoietic-specific activator of Rac, compromises engraftment of transplanted adult HSPCs without affecting steady-state hematopoiesis in adult animals. Here, we show that Vav1-/- fetal HSPCs can appropriately seed hematopoietic tissues during ontogeny but cannot engraft into lethally irradiated recipients. We demonstrate that the engraftment defect of Vav1-/- HSPCs is abrogated in the absence of irradiation and demonstrate that Vav1 is critical for the response of HSPCs to the proinflammatory cytokine interleukin-11 (IL-11) that is upregulated in the marrow of irradiated recipients. Vav1-/- HSPCs display abnormal proliferative responses to IL-11 in vitro and dysregulated activation of pathways critical to engraftment of HSPCs. The engraftment of Vav1-/- HSPCs can be partially rescued in irradiated recipients treated with an anti-IL-11 antibody. These data suggest that HSPCs may respond to different functional demands by selective usage of the IL-11-Vav-Rac pathway, contextualizing further the recent view that HSPCs capable of reconstituting the blood system following transplantation might be distinct from those supporting hematopoiesis during homeostatic conditions. Stem Cells 2018; 36:446-457.

CMV-Specific T-cell Responses at Older Ages: Broad Responses With a Large Central Memory Component May Be Key to Long-term Survival.

Cytomegalovirus (CMV) infection sometimes causes large expansions of CMV-specific T cells, particularly in older people. This is believed to undermine immunity to other pathogens and to accelerate immunosenescence. While multiple different CMV proteins are recognized, most publications on age-related T-cell expansions have focused on dominant target proteins UL83 or UL123, and the T-cell activation marker interferon-γ (IFN-γ). We were concerned that this narrow approach might have skewed our understanding of CMV-specific immunity at older ages. We have, therefore, widened the scope of analysis to include in vitro-induced T-cell responses to 19 frequently recognized CMV proteins in "young" and "older" healthy volunteers and a group of "oldest old" long-term survivors (>85 years of age). Polychromatic flow cytometry was used to analyze T-cell activation markers (CD107, CD154, interleukin-2 [IL-2], tumor necrosis factor [TNF], and IFN-γ) and memory phenotypes (CD27, CD45RA). The older group had, on average, larger T-cell responses than the young, but, interestingly, response size differences were relatively smaller when all activation markers were considered rather than IFN-γ or TNF alone. The oldest old group recognized more proteins on average than the other groups, and had even bigger T-cell responses than the older group with a significantly larger central memory CD4 T-cell component.

First epidemiological and phylogenetic analysis of Hepatitis B virus infection in migrants from Mali.

The armed conflict in Mali caused a migration crisis since 2012. Most Malian refugees were in Italy. In Sub-Saharan Africa, the seroprevalence of anti-HBV antibodies is particularly high. Genotype E is the most prevalent throughout a crescent covering area from Angola to Senegal, including Mali. We report 16 HBV positive individual from 136 Malian asylum seekers in order to investigate the genetic diversity of HBV in this population. Sequencing and phylogenetic analysis has been used. The HBV genotype E isolates from Mali did not cluster together but were intermixed, with the other African sequences. Only three supported clade were evidenced and closely related to sequences from Burkina Faso. The estimated evolutionary rate was 9.29 × 104 . The root of the tree dated back to February 2008 in (95% HPD: 2006-2011). From this ancestor six main statistically supported clusters (pp > 0.80) were identified. The most recent Clade dated back to May 2015. The BSP showed that the effective number of infections softly increased from 2011 to the 2015. Phylogenetic analysis helped in understanding how two on sixteen individuals, have been infected in Italy, and give an important improvement in prevention campaigns and monitoring of the viral infection in migrants. J. Med. Virol. 89:639-646, 2017. © 2016 Wiley Periodicals, Inc.

Functional Diversity of Cytomegalovirus-Specific T Cells Is Maintained in Older People and Significantly Associated With Protein Specificity and Response Size.

BACKGROUND: Parallel upregulation of several T-cell effector functions (ie, polyfunctionality) is believed to be critical for the protection against viruses but thought to decrease in large T-cell expansions, in particular at older ages. The factors determining T-cell polyfunctionality are incompletely understood. Here we revisit the question of cytomegalovirus (CMV)-specific T-cell polyfunctionality, including a wide range of T-cell target proteins, response sizes, and participant ages. METHODS: Polychromatic flow cytometry was used to analyze the functional diversity (ie, CD107, CD154, interleukin 2, tumor necrosis factor, and interferon γ expression) of CD4+ and CD8+ T-cell responses to 19 CMV proteins in a large group of young and older United Kingdom participants. A group of oldest old people (age >85 years) was included to explore these parameters in exceptional survivors. Polyfunctionality was assessed for each protein-specific response subset, by subset and in aggregate, across all proteins by using the novel polyfunctionality index. RESULTS: Polyfunctionality was not reduced in healthy older people as compared to young people. However, it was significantly related to target protein specificity. For each protein, it increased with response size. In the oldest old group, overall T-cell polyfunctionality was significantly lower. DISCUSSION: Our results give a new perspective on T-cell polyfunctionality and raise the question of whether maintaining polyfunctionality of CMV-specific T cells at older ages is necessarily beneficial.

Health profile and disease determinants among asylum seekers: a cross-sectional retrospective study from an Italian reception centre.

BACKGROUND: Data on diseases' determinants and health status of asylum seekers (ASs) are limited. METHODS: We performed a cross-sectional retrospective study in a large ASs centre in Italy. Data were collected during a 1-year period. Descriptive statistics were calculated. A χ(2) test was used to assess the association between socio-demographics characteristics of ASs and screening test results. A multiple logistic regression analysis was performed to identify diseases' predictors by using ICD-10 diagnoses classification as outcome variable, socio-demographic characteristics as independent variable and visits' number as confounding variable. RESULTS: Overall, data on 792 ASs (mean age 27 years, 80% males, 58% from Africa) were assessed, 43% underwent voluntary infectious diseases screening and 2843 diagnoses were recorded. The most frequent diagnoses were: respiratory diseases, symptoms/signs not elsewhere classified, digestive diseases and infectious diseases. Gender was the most frequent predictor of ICD-10 diagnoses, while African origin, civil status and education were, respectively, predictive of cardiovascular and infectious diseases, genitourinary diseases and pregnancy-related disorders. Higher mean age was associated with syphilis, HIV and HCV infection and African origin with HIV infection. CONCLUSIONS: Communicable diseases were not prevalent in the ASs population we analysed. A stronger cultural mediation support is needed to facilitate prevention, access and continuity of care for ASs.

Cytomegalovirus coinfection is associated with an increased risk of severe non-AIDS-defining events in a large cohort of HIV-infected patients.

BACKGROUND: Chronic cytomegalovirus (CMV) infection has been associated with immunosenescence and immunoactivation in the general population. In human immunodeficiency virus type 1 (HIV-1)-infected people, CMV coinfection, in addition to residual HIV replication and microbial translocation, has been proposed as a key factor in sustaining immune activation, even in individuals with a controlled HIV load. METHODS: Patients from the ICONA Study with at least 1 CMV immunoglobulin G (IgG) test available without active CMV disease were included in the analysis. AIDS-defining event or AIDS-related death and severe non-AIDS-defining event or non-AIDS-related death were taken as clinical progression end points. Independent predictors of CMV were identified by multivariable logistic regression. Probabilities of reaching the end points were estimated by survival analyses. RESULTS: A total of 6111 subjects were included, of whom 5119 (83.3%) were CMV IgG positive at baseline. Patients with CMV IgG positivity at baseline were more likely to develop a severe non-AIDS-defining event/non-AIDS-related death (adjusted hazard ratio [HR], 1.53 [95% confidence interval {CI}, 1.08-2.16]. In particular, CMV seropositivity was an independent risk factor for cardiovascular and cerebrovascular diseases (adjusted HR, 2.27 [95% CI, .97-5.32]). CONCLUSIONS: In our study population, CMV/HIV coinfection was associated with the risk of severe non-AIDS-defining events/non-AIDS-related death, especially with cardiovascular and cerebrovascular events, independently of other prognostic factors. This finding supports a potential independent role of CMV coinfection in vascular/degenerative organ disorders in HIV-infected subjects.

The Rac GTPase effector p21-activated kinase is essential for hematopoietic stem/progenitor cell migration and engraftment.

The p21-activated kinases (Paks) are serine/threonine kinases that are major effectors of the Rho guanosine 5'\x{2011}triphosphatase, Rac, and Cdc42. Rac and Cdc42 are known regulators of hematopoietic stem and progenitor cell (HSPC) function, however, a direct role for Paks in HSPCs has yet to be elucidated. Lin(-)Sca1(+)c-kit(+) (LSK) cells from wild-type mice were transduced with retrovirus expressing Pak inhibitory domain (PID), a well-characterized inhibitor of Pak activation. Defects in marrow homing and in vitro cell migration, assembly of the actin cytoskeleton, proliferation, and survival were associated with engraftment failure of PID-LSK. The PID-LSK demonstrated decreased phosphorylation of extracellular signal-regulated kinase (ERK), whereas constitutive activation of ERK in these cells led to rescue of hematopoietic progenitor cell proliferation in vitro and partial rescue of Pak-deficient HSPC homing and engraftment in vivo. Using conditional knock-out mice, we demonstrate that among group A Paks, Pak2(-/-) HSPC show reduced homing to the bone marrow and altered cell shape similar to PID-LSK cells in vitro and are completely defective in HSPC engraftment. These data demonstrate that Pak proteins are key components of multiple engraftment-associated HSPC functions and play a direct role in activation of ERK in HSPCs, and that Pak2 is specifically essential for HSPC engraftment.