Improved outcome of allogeneic transplantation in older patients treated for myeloid malignancies using post transplantation cyclophosphamide and reduced duration of immune suppression

BACKGROUND

Allogeneic stem cell transplantation (alloSCT) offers curative potential for older patients with myeloid malignancies. We evaluated the efficacy and safety of alloSCT using post-transplantation cyclophosphamide (PTCy) in combination with a very short duration of immune suppression (IS) in this population.

METHODS

We retrospectively analyzed 92 consecutive patients aged 65 years and older who underwent an alloSCT for myeloid malignancies between February 2018 and December 2022 at our institution. Data on patient characteristics, treatment modalities, and outcomes were collected.

RESULTS

Ninety-two patients received an alloSCT with PTCy-based GVHD prophylaxis. The majority had minimal comorbidities and were diagnosed with acute myeloid leukemia (AML). Patients mostly received conditioning regimens with low to intermediate TCI scores. In 43% of patients, IS could be permanently stopped at day +90, resulting in a median time of IS of 2.93 months in high-risk patients. At a median follow-up of 21.3 months, the 1- and 2-year overall survival rates were 89% and 87%, respectively. Relapse-free survival rates were 88% and 84% at 1 and 2 years, respectively. The 1- and 2-year cumulative incidences of relapse were 8% and 13%, while transplant-related mortality (TRM) estimates were 9% at both time points. Acute GVHD grade 3-4 occurred in 7% within the first 180 days and severe chronic GVHD in 6% of patients. This all resulted in a 1- and 2-year graft versus host and relapse free survival (GRFS) of 74% and 70%, respectively.

CONCLUSION

AlloSCT using PTCy in combination with a short duration of IS in older patients with myeloid malignancies demonstrates favorable survival outcomes due to low relapse rates and a low TRM. The low incidence of relapse and acceptable rates of graft-versus-host disease suggest the efficacy and safety of this approach. Further studies are warranted to validate these findings and optimize transplant strategies for older patients with myeloid malignancies.

R-miniCHOP versus R-CHOP in elderly patients with diffuse large B-cell lymphoma: A propensity matched population-based study

For elderly frail patients with diffuse large B-cell lymphoma (DLBCL), an attenuated chemo-immunotherapy strategy of rituximab, cyclophosphamide, doxorubicin, vincristine and prednisolone (R-miniCHOP) was introduced as a treatment option as from 2014 onward in the Netherlands. Although R-miniCHOP is more tolerable, reduction of chemotherapy could negatively affect survival compared to R-CHOP. The aim of this analysis was to assess survival of patients treated with R-miniCHOP compared to R-CHOP. DLBCL patients ≥65 years, newly diagnosed in 2014-2020, who received ≥1 cycle of R-miniCHOP or R-CHOP were identified in the Netherlands Cancer Registry, with survival follow-up through 2022. Patients were propensity-score-matched for baseline characteristics. Main endpoints were progression-free survival (PFS), overall survival (OS), and relative survival (RS). The use of R-miniCHOP in DLBCL increased from 2% in 2014 to 15% in 2020. In total, 384 patients treated with R-miniCHOP and 384 patients treated with R-CHOP were included for comparison (median age; 81 years, stage 3-4; 68%). The median number of R-(mini)CHOP cycles was 6 (range, 1-8). The 2-year PFS, OS and RS were inferior for patients treated with R-miniCHOP compared to R-CHOP (PFS 51% vs. 68%, p < .01; OS 60% vs. 75%, p < .01; RS 69% vs. 86%, p < .01). In multivariable analysis, patients treated with R-miniCHOP had higher risk of all-cause mortality compared to patients treated with R-CHOP (HR 1.73; 95%CI, 1.39-2.17). R-miniCHOP is effective for most elderly patients. Although survival is inferior compared to R-CHOP, the use of R-miniCHOP as initial treatment is increasing. Therefore, fitness needs to be carefully weighed in treatment selection.

[Clonal hematopoiesis: a risk factor for leukemia and cardiovascular disease?]

Upon ageing, hematopoietic stem or progenitor cells harboring acquired leukemia-associated mutations may expand clonally and become detectable in peripheral blood. So-called clonal hematopoiesis may be detected in 5-55% of (otherwise healthy) individuals aged ≥ 70 years. Clonal hematopoiesis is associated with a higher risk of developing hematological neoplasms, although most individuals never develop malignant disease. Surprisingly, clonal hematopoiesis is also recognized as a new cardiovascular risk factor. Specific patient categories may be at higher risk for the consequences of clonal hematopoiesis. For future risk stratification, there is a need to distinguish high-risk clonal hematopoiesis from 'physiological' ageing processes. In this article we summarize current knowledge on clonal hematopoiesis and its clinical implications. Given the widespread application of next-generation sequencing in routine diagnostics, multidisciplinary recommendations for clinical management of individuals with detected clonal hematopoiesis should be developed.

Lenalidomide added to standard intensive treatment for older patients with AML and high-risk MDS

More effective treatment modalities are urgently needed in patients with acute myeloid leukemia (AML) of older age. We hypothesized that adding lenalidomide to intensive standard chemotherapy might improve their outcome. After establishing a safe lenalidomide, dose elderly patients with AML were randomly assigned in this randomized Phase 2 study (n = 222) to receive standard chemotherapy ("3 + 7") with or without lenalidomide at a dose of 20 mg/day 1-21. In the second cycle, patients received cytarabine 1000 mg/m² twice daily on days 1-6 with or without lenalidomide (20 mg/day 1-21). The CR/CRi rates in the two arms were not different (69 vs. 66%). Event-free survival (EFS) at 36 months was 19% for the standard arm versus 21% for the lenalidomide arm and overall survival (OS) 35% vs. 30%, respectively. The frequencies and grade of adverse events were not significantly different between the treatment arms. Cardiovascular toxicities were rare and equally distributed between the arms. The results of the present study show that the addition of lenalidomide to standard remission induction chemotherapy does not improve the therapeutic outcome of older AML patients. This trial is registered as number NTR2294 in The NederlandsTrial Register (www.trialregister.nl).

Association of vitamin B12, methylmalonic acid, and functional parameters

INTRODUCTION

Diagnosis of vitamin B12 deficiency is difficult, as there is no conclusive single test for this disorder. We evaluated the association of serum B12 and methylmalonic acid (MMA) with haematologic parameters and physical and cognitive functioning in an effort to use such clinical parameters to improve the interpretation of serum values.

METHODS

We used data of participants > 19 years of age from NHANES 2011-2012 and 2013-2014, a cross-sectional survey in the United States. Functional status was assessed with questionnaires on current health condition, disability, hospital utilisation, cognitive functioning, mental health and depression, and physical functioning. Muscle strength assessed with a handgrip dynamometer was used as a performance parameter. Results were evaluated both for the entire population and participants of Western European descent. Because renal function influences MMA concentrations and is a proxy for both frailty and comorbidity, all results were additionally stratified for individuals with normal vs impaired renal function (eGFR < 60 ml/min).

RESULTS

In total, data of 9645 participants (mean age 49 (SD 17) years, 49.3% males) were included. Out of all participants with serum B12 < 140, 140-300, and 301-1000 pmol/l, 56.2%, 13.5%, and 4.1%, respectively had elevated MMA. MMA concentrations were more strongly associated with poor functional status and physical performance than serum B12. We identified a significant and independent association of MMA concentrations, as well as haemoglobin and co-morbidity with muscle strength.

CONCLUSIONS/INTERPRETATIONS

A large proportion of individuals with a decreased serum B12 concentration still has normal MMA concentrations. Elevated MMA concentrations were more strongly associated with poor functional performance than serum B12.

Ring sideroblasts in AML are associated with adverse risk characteristics and have a distinct gene expression pattern

Ring sideroblasts (RS) emerge as result of aberrant erythroid differentiation leading to excessive mitochondrial iron accumulation, a characteristic feature for myelodysplastic syndromes (MDS) with mutations in the spliceosome gene SF3B1. However, RS can also be observed in patients diagnosed with acute myeloid leukemia (AML). The objective of this study was to characterize RS in patients with AML. Clinically, RS-AML is enriched for ELN adverse risk (55%). In line with this finding, 35% of all cases had complex cytogenetic aberrancies, and TP53 was most recurrently mutated in this cohort (37%), followed by DNMT3A (26%), RUNX1 (25%), TET2 (20%), and ASXL1 (19%). In contrast to RS-MDS, the incidence of SF3B1 mutations was low (8%). Whole-exome sequencing and SNP array analysis on a subset of patients did not uncover a single genetic defect underlying the RS phenotype. Shared genetic defects between erythroblasts and total mononuclear cell fraction indicate common ancestry for the erythroid lineage and the myeloid blast cells in patients with RS-AML. RNA sequencing analysis on CD34+ AML cells revealed differential gene expression between RS-AML and non RS-AML cases, including genes involved in megakaryocyte and erythroid differentiation. Furthermore, several heme metabolism-related genes were found to be upregulated in RS- CD34+ AML cells, as was observed in SF3B1mut MDS. These results demonstrate that although the genetic background of RS-AML differs from that of RS-MDS, they have certain downstream effector pathways in common.

Diagnostic performance of FDG-PET/CT of post-transplant lymphoproliferative disorder and factors affecting diagnostic yield

Purpose

Post-transplant lymphoproliferative disorder (PTLD) is a serious complication after solid organ and hematopoietic stem cell transplantation, requiring a timely and accurate diagnosis. In this study, we evaluated the diagnostic performance of FDG-PET/CT in patients with suspected PTLD and examined if lactate dehydrogenase (LDH) levels, Epstein-Barr virus (EBV) load, or timing of FDG-PET/CT relate to detection performance of FDG-PET/CT.

Methods

This retrospective study included 91 consecutive patients with clinical suspicion of PTLD and a total of 97 FDG-PET/CT scans within an 8-year period. Pathology reports and a 2-year follow-up were used as the reference standard. Diagnostic performance of FDG-PET/CT for detection of PTLD as well as logistic regression analysis for factors expected to affect diagnostic yield were assessed.

Results

The diagnosis of PTLD was established in 34 patients (35%). Fifty-seven FDG-PET/CT scans (59%) were true negative, 29 (30%) were true positive, 6 (6%) false positive, and 5 (5%) false negative. Sensitivity of FDG-PET/CT for the detection of PTLD was 85%, specificity 90%, positive predictive value 83%, and negative predictive value 92%, with good inter-observer variability (k = 0.78). Of the parameters hypothesized to be associated with a true positive FDG-PET/CT result for the diagnosis of PTLD, only LDH was statistically significant (OR 1.03, p = 0.04).

Conclusion

FDG-PET/CT has a good diagnostic performance in patients suspected of PTLD, with a good inter-observer agreement. Only LDH levels seemed to influence the detection performance of FDG-PET/CT. EBV-DNA load and timing of FDG-PET/CT after transplantation did not affect FDG-PET/CT diagnostic yield.

Comparative value of post-remission treatment in cytogenetically normal AML subclassified by NPM1 and FLT3-ITD allelic ratio

Post-remission treatment (PRT) in patients with cytogenetically normal (CN) acute myeloid leukemia (AML) in first complete remission (CR1) is debated. We studied 521 patients with CN-AML in CR1, for whom mutational status of NPM1 and FLT3-ITD was available, including the FLT3-ITD allelic ratio. PRT consisted of reduced intensity conditioning (RIC) allogeneic hematopoietic stem cell transplantation (alloHSCT) (n=68), myeloablative conditioning (MAC) alloHSCT (n=137), autologous hematopoietic stem cell transplantation (autoHSCT) (n=168) or chemotherapy (n=148). Favorable overall survival (OS) was found for patients with mutated NPM1 without FLT3-ITD (71±4%). Outcome in patients with a high FLT3-ITD allelic ratio appeared to be very poor with OS and relapse-free survival (RFS) of 23±8% and 12±6%, respectively. Patients with wild-type NPM1 without FLT3-ITD or with a low allelic burden of FLT3-ITD were considered as intermediate-risk group because of similar OS and RFS at 5 years, in which PRT by RIC alloHSCT resulted in better OS and RFS as compared with chemotherapy (hazard ratio (HR) 0.56, P=0.022 and HR 0.50, P=0.004, respectively) or autoHSCT (HR 0.60, P=0.046 and HR 0.60, P=0.043, respectively). The lowest cumulative incidence of relapse (23±4%) was observed following MAC alloHSCT. These results suggest that alloHSCT may be preferred in patients with molecularly intermediate-risk CN-AML, while the choice of conditioning type may be personalized according to risk for non-relapse mortality.

Ruxolitinib in corticosteroid-refractory graft-versus-host disease after allogeneic stem cell transplantation: a multicenter survey

Despite major improvements in allogeneic hematopoietic cell transplantation over the past decades, corticosteroid-refractory (SR) acute (a) and chronic (c) graft-versus-host disease (GVHD) cause high mortality. Preclinical evidence indicates the potent anti-inflammatory properties of the JAK1/2 inhibitor ruxolitinib. In this retrospective survey, 19 stem cell transplant centers in Europe and the United States reported outcome data from 95 patients who had received ruxolitinib as salvage therapy for SR-GVHD. Patients were classified as having SR-aGVHD (n=54, all grades III or IV) or SR-cGVHD (n=41, all moderate or severe). The median number of previous GVHD-therapies was 3 for both SR-aGVHD (1-7) and SR-cGVHD (1-10). The overall response rate was 81.5% (44/54) in SR-aGVHD including 25 complete responses (46.3%), while for SR-cGVHD the ORR was 85.4% (35/41). Of those patients responding to ruxolitinib, the rate of GVHD-relapse was 6.8% (3/44) and 5.7% (2/35) for SR-aGVHD and SR-cGVHD, respectively. The 6-month-survival was 79% (67.3-90.7%, 95% confidence interval (CI)) and 97.4% (92.3-100%, 95% CI) for SR-aGVHD and SR-cGVHD, respectively. Cytopenia and cytomegalovirus-reactivation were observed during ruxolitinib treatment in both SR-aGVHD (30/54, 55.6% and 18/54, 33.3%) and SR-cGVHD (7/41, 17.1% and 6/41, 14.6%) patients. Ruxolitinib may constitute a promising new treatment option for SR-aGVHD and SR-cGVHD that should be validated in a prospective trial.

Azacitidine results in comparable outcome in newly diagnosed AML patients with more or less than 30% bone marrow blasts

The efficacy of azacitidine has been demonstrated in acute myeloid leukemia (AML) patients with 20-30% bone marrow (BM) blasts, but limited data is available on patients with ≥30% blasts. We analyzed 55 newly diagnosed AML patients, treated with azacitidine. The overall response rate was 42%. Median overall survival (OS) was 12.3 months. We confirmed poor-risk cytogenetics, therapy-related AML, performance score ≥2, and white blood cell count ≥15×10(9)/L as independent adverse predictors for OS. The BM blast percentage, however, had no impact on OS (P=0.55). In conclusion, administration of azacitidine is effective in AML patients with 20-30% and >30% BM blasts.

The circulating platelet count is not dictated by the liver, but may be determined in part by the bone marrow: analyses from human liver and stem cell transplantations

BACKGROUND

The platelet count varies considerably between individuals, but within an individual the platelet count is remarkably stable over time. Mechanisms controlling the platelet count are not yet established.

OBJECTIVE

In the present study, we tested the hypothesis that the liver is important in controlling the circulating platelet count, as the liver is the main producer of thrombopoietin.

METHODS

We compared the platelet count prior to and after liver transplantation in >250 patients transplanted for familial amyloidotic polyneuropathy (FAP). In contrast to most patients undergoing liver transplantation, patients with FAP have normal liver function before transplantation. Furthermore, we compared platelet counts in 89 living liver donors with the platelet count in the recipients of these grafts. Finally we compared platelet counts in donor-recipient pairs of hematopoietic stem cells.

RESULTS AND CONCLUSIONS

The platelet count prior to transplantation correlated with the platelet count at 3 or 12 months after transplantation in patients with FAP (r=0.48, P<0.0001 at 3 months, r=0.39, P<0.0001 at 12 months), whereas the platelet count in a living liver donor did not correlate with the platelet count in the recipient at 3 or 12 months after transplantation (r=0.16, P=0.26 at 3 months, r=0.11, P=0.30 at 12 months). The platelet count of related donors of hematopoietic stem cells correlated with the platelet count in the recipient after transplantation (r=0.25, P=0.011).

CONCLUSIONS

These results suggest that the liver, in spite of being the prime producer of thrombopoietin, does not dictate the circulating platelet count, whereas the bone marrow does appear to play a role.

Gene expression profiling in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a heterogeneous disease characterised by clonal malignant haematopoiesis with a differentiation arrest and excessive proliferation of leukaemic blasts. Over the past decades, the heterogeneity of AML has been illustrated by evolving classifications based on morphology (French-American-British classification (FAB classification), cytogenetic abnormalities (e.g. t(8&semi;21), monosomies etc.), phenotype and÷or molecular abnormalities (e.g. Fms-like tyrosine kinase 3 gene internal tandem duplication (FLT3-ITD), mutations in nucleophosmin 1 (NPM1) and the transcription factor CCAAT ÷enhancer binding protein a (CEBPA), etc.). The current World Health Organisation (WHO) 2008 classification has integrated these classification modalities. Clinically, dissection of AML into various subtypes allows better survival prediction, but has still limited impact on treatment strategies, with the exception of all-trans retinoic acid treatment for AML-M3 and no allogeneic haematopoietic cell transplantation in complete remission (CR1) for patients with normal karyotype bearing an NPM1 mutation without FLT3-ITD. However, enhanced understanding of the molecular biology of AML will likely result in more 'tailor-made' therapies, for example by adding specific tyrosine kinase inhibitors to standard chemotherapy. In this review, we summarise the variables currently used to classify AML. Specifically, the contribution of microarrays in classification, prognosis and understanding of pathobiology of AML is discussed.

Bleomycin and scuba diving: to dive or not to dive?

Bleomycin is to treat patients with testicular cancer and lymphoma. Bleomycin can bind to DNA and chelate iron. The resulting complex can form an intermediate capable of interacting with oxygen to produce reactive oxygen species, particularly superoxide. Administrating high-inspired oxygen concentrations (e.g. during anaesthesia or acute illness) has been reported to exacerbate pulmonary injury. The duration of risk after bleomycin chemotherapy is unknown. Here we discuss our advice to a young male patient, who was successfully treated with bleomycin for testicular cancer, concerning the safety to return to scuba diving. Since scuba divers are exposed to high partial oxygen pressures (depending on the depth of the dive) we discouraged this patient from resuming scuba diving.

Enhancement of polymorphonuclear cell-mediated tumor cell killing on simultaneous engagement of fcgammaRI (CD64) and fcalphaRI (CD89)

Antibodies can efficiently induce antitumor responses via recruitment of Fc receptor-bearing cytotoxic cells. Polymorphonuclear (PMN) cells represent attractive effector cells for antibody-directed immunotherapy. This, because activated PMN cells coexpress the class I receptors for IgG (FcgammaRI, CD64) and IgA (FcalphaRI, CD89), which are potent cytotoxic trigger molecules. Both receptors, however, require the FcR gamma chain for signaling. In this study, we show that FcgammaRI and FcalphaRI can trigger function independently of one another and do not cross-compete for the FcR gamma chain. FcalphaRI proved more efficient in initiating early signaling events and effector functions, such as redirected tumor cell killing and generation of superoxide. In addition, simultaneous engagement of FcgammaRI and FcalphaRI resulted in enhanced tumor cell lysis. These data support the development of concepts in which both FcgammaRI and FcalphaRI on PMN cells are targeted for tumor therapy.

Wnt/(beta)-catenin signaling regulates the expression of the homeobox gene Cdx1 in embryonic intestine

During mammalian development, the Cdx1 homeobox gene exhibits an early period of expression when the embryonic body axis is established, and a later period where expression is restricted to the embryonic intestinal endoderm. Cdx1 expression is maintained throughout adulthood in the proliferative cell compartment of the continuously renewed intestinal epithelium, the crypts. In this study, we provide evidence in vitro and in vivo that Cdx1 is a direct transcriptional target of the Wnt/(beta)-catenin signaling pathway. Upon Wnt stimulation, expression of Cdx1 can be induced in mouse embryonic stem (ES) cells as well as in undifferentiated rat embryonic endoderm. Tcf4-deficient mouse embryos show abrogation of Cdx1 protein in the small intestinal epithelium, making Tcf4 the likely candidate to transduce Wnt signal in this part of gut. The promoter region of the Cdx1 gene contains several Tcf-binding motifs, and these bind Tcf/Lef1/(beta)-catenin complexes and mediate (beta)-catenin-dependent transactivation. The transcriptional regulation of the homeobox gene Cdx1 in the intestinal epithelium by Wnt/(beta)-catenin signaling underlines the importance of this signaling pathway in mammalian endoderm development.

Antitumor immune effector mechanisms recruited by phage display-derived fully human IgG1 and IgA1 monoclonal antibodies

We have constructed a recombinant, fully human IgA1 monoclonal antibody, UBS-54/IgA1, against the tumor-associated Ep-CAM molecule and compared its tumor-killing capacity with its IgG1 counterpart in in vitro assays. The data show that phage display-derived fully human IgA1 antibodies efficiently recruit immune effector cells that express the Fc receptor for IgA, FcalphaRI (CD89). UBS-54/IgA1-mediated killing of tumor cells by isolated polymorphonuclear cells (PMNs) and in whole blood was found to proceed without the necessity to preactivate effector cells with cytokines. In addition, the IgA1 anti-Ep-CAM human monoclonal antibody (huMab) triggered phagocytosis of tumor cells by monocyte-derived macrophages. Strikingly, simultaneous addition of IgA1 and IgG1 anti-Ep-CAM antibodies did not result in enhancement of tumor cell killing unless the effector cells were stimulated with granulocyte colony-stimulating factor. The lack of an additive effect could be attributed to an inhibitory effect of IgG on IgA-mediated tumor cell killing through binding of IgG1 to the inhibitory FcgammaRIIb receptor expressed by PMNs. These results show that IgA1 antitumor huMabs are capable of recruiting the large population of peripheral blood PMNs for tumor cell killing. This population is not effectively recruited by IgG type antibodies, currently the antibodies most frequently used for clinical application. In addition, the data suggest that a combination of IgG1 and IgA1 antitumor huMabs may collaborate in tumor cell killing in patients treated with granulocyte colony-stimulating factor.

Synergy between tumor suppressor APC and the beta-catenin-Tcf4 target Tcf1

Mutations in APC or beta-catenin inappropriately activate the transcription factor Tcf4, thereby transforming intestinal epithelial cells. Here it is shown that one of the target genes of Tcf4 in epithelial cells is Tcf1. The most abundant Tcf1 isoforms lack a beta-catenin interaction domain. Tcf1(-/-) mice develop adenomas in the gut and mammary glands. Introduction of a mutant APC allele into these mice substantially increases the number of these adenomas. Tcf1 may act as a feedback repressor of beta-catenin-Tcf4 target genes and thus may cooperate with APC to suppress malignant transformation of epithelial cells.

Restricted high level expression of Tcf-4 protein in intestinal and mammary gland epithelium

Tcf-4 is a member of the Tcf/Lef family of transcription factors that interact functionally with beta-catenin to mediate Wnt signaling in vertebrates. We have previously demonstrated that the tumor suppressor function of APC in the small intestine is mediated via regulation of Tcf-4/beta-catenin transcriptional activity. To gain further insight into the role of Tcf-4 in development and carcinogenesis we have generated several mouse monoclonal antibodies, one of which is specific for Tcf-4 and another of which recognizes both Tcf-3 and Tcf-4. Immunohistochemistry performed with the Tcf 4- specific monoclonal antibody revealed high levels of expression in normal intestinal and mammary epithelium and carcinomas derived therefrom. Additional sites of Tcf-3 expression, as revealed by staining with the Tcf-3/-4 antibody, occurred only within the stomach epithelium, hair follicles, and keratinocytes of the skin. A temporal Tcf-4 expression gradient was observed along the crypt-villus axis of human small intestinal epithelium: strong Tcf-4 expression was present within the crypts of early (week 16) human fetal small intestine, with the villi showing barely detectable Tcf-4 protein levels. Tcf-4 expression levels increased dramatically on the villi of more highly developed (week 22) fetal small intestine. We conclude that Tcf-4 exhibits a highly restricted expression pattern related to the developmental stage of the intestinal epithelium. The high levels of Tcf-4 expression in mammary epithelium and mammary carcinomas may also indicate a role in the development of this tissue and breast carcinoma.

Depletion of epithelial stem-cell compartments in the small intestine of mice lacking Tcf-4

Mutations of the genes encoding APC or beta-catenin in colon carcinoma induce the constitutive formation of nuclear beta-catenin/Tcf-4 complexes, resulting in activated transcription of Tcf target genes. To study the physiological role of Tcf-4 (which is encoded by the Tcf7/2 gene), we disrupted Tcf7/2 by homologous recombination. Tcf7/2-/- mice die shortly after birth. A single histopathological abnormality was observed. An apparently normal transition of intestinal endoderm into epithelium occurred at approximately embryonic day (E) 14.5. However, no proliferative compartments were maintained in the prospective crypt regions between the villi. As a consequence, the neonatal epithelium was composed entirely of differentiated, non-dividing villus cells. We conclude that the genetic program controlled by Tcf-4 maintains the crypt stem cells of the small intestine. The constitutive activity of Tcf-4 in APC-deficient human epithelial cells may contribute to their malignant transformation by maintaining stem-cell characteristics.