Low-dose total body irradiation-based regimens as a preparative regimen for allogeneic haematopoietic cell transplantation in acute myelogenous leukaemia

Reduced intensity conditioning allogeneic hematopoietic cell transplantation for adult acute myeloid leukemia in complete remission - a review from the Acute Leukemia Working Party of the EBMT

Acute myeloid leukemia is the most common indication for an allogeneic hematopoietic cell transplant. The introduction of reduced intensity conditioning has expanded the recipient pool for transplantation, which has importantly made transplant an option for the more commonly affected older age groups. Reduced intensity conditioning allogeneic transplantation is currently the standard of care for patients with intermediate or high-risk acute myeloid leukemia and is now most often employed in older patients and those with medical comorbidities. Despite being curative for a significant proportion of patients, post-transplant relapse remains a challenge in the reduced intensity conditioning setting. Herein we discuss the studies that demonstrate the feasibility of reduced intensity conditioning allogeneic transplants, compare the outcomes of reduced intensity conditioning versus chemotherapy and conventional myeloablative conditioning regimens, describe the optimal donor and stem cell source, and consider the impact of post-remission consolidation, comorbidities, center experience, and more intensive (reduced toxicity conditioning) regimens on outcomes. Additionally, we discuss the need for further prospective studies to optimize transplant outcomes.

CD123 redirected multiple virus-specific T cells for acute myeloid leukemia

Hematopoietic stem cell transplantation (HSCT) has been increasingly used as a curative treatment for acute myeloid leukemia (AML). However, relapse rates after HSCT in complete remission (CR) are reported between 30% and 70%. In addition, numerous studies suggested that secondary viral infection from a variety of viruses including Epstein-Barr virus (EBV), adenovirus (Adv), and cytomegalovirus (CMV) are among the most common causes of death post-HSCT. Currently, chimeric antigen receptor (CAR)-based T cells have been developed to treat AML in clinical studies, while virus-specific cytotoxic T cells (VST) have been proven to be able to effectively prevent or treat viral infection after HSCT. Thus it would be desirable to develop T cells with the ability of simultaneously targeting AML relapse and viral infection. In this article, we now describe the generation of VST cells that are engineered to express CAR for a specific AML cell-surface antigen CD123 (CD123-CAR-VST). Using Dendritic cells (DCs) pulsed with EBV, Adv, and CMV peptides as sources of viral antigens, we generated VST from A2 donor peripheral mononuclear cells (PBMC). VST were then transduced with retroviral vector encoding CD123-CAR to generate CD123-CAR-VST. We demonstrated that CD123-CAR-VST recognized EBV, Adv, and CMV epitopes and had HLA-restricted virus-specific cytotoxic effector function against EBV target. In addition, CD123-CAR-VST retained the specificity against CD123-positive AML cell lines such as MOLM13 and THP-1 in vitro. Thus our results suggested that CD123-CAR-VST might be a valuable candidate to simultaneously prevent or treat relapse and viral infection in AML HSCT recipients.

miR-363-5p regulates endothelial cell properties and their communication with hematopoietic precursor cells

Recent findings have shown that the blood vessels of different organs exert an active role in regulating organ function. In detail, the endothelium that aligns the vasculature of most organs is fundamental in maintaining organ homeostasis and in promoting organ recovery following injury. Mechanistically, endothelial cells (EC) of tissues such as the liver, lungs or the bone marrow (BM) have been shown to produce “angiocrine” factors that promote organ recovery and restore normal organ function. Controlled production of angiocrine factors following organ injury is therefore essential to promote organ regeneration and to restore organ function. However, the molecular mechanisms underlying the coordinated production and function of such “angiocrine” factors are largely undisclosed and were the subject of the present study. In detail, we identified for the first time a microRNA (miRNA) expressed by BM EC that regulates the expression of angiocrine genes involved in BM recovery following irradiation. Using a microarray-based approach, we identified several miRNA expressed by irradiated BMEC. After validating the variations in miRNA expression by semi-quantitative PCR, we chose to study further the ones showing consistent variations between experiments, and those predicted to regulate (directly or indirectly) angiogenic and angiocrine factors. Of the mi-RNA that were chosen, miR-363-5p (previously termed miR-363*) was subsequently shown to modulate the expression of numerous EC-specific genes including some angiocrine factors. By luciferase reporter assays, miR-363-5p is shown to regulate the expression of angiocrine factors tissue inhibitor of metalloproteinases-1 (Timp-1) and thrombospondin 3 (THBS3) at post-transcriptional level. Moreover, miR-363-5p reduction using anti-miR is shown to affect EC angiogenic properties (such as the response to angiogenic factors stimulation) and the interaction between EC and hematopoietic precursors (particularly relevant in a BM setting). miR-363-5p reduction resulted in a significant decrease in EC tube formation on matrigel, but increased hematopoietic precursor cells adhesion onto EC, a mechanism that is shown to involve kit ligand-mediated cell adhesion. Taken together, we have identified a miRNA induced by irradiation that regulates angiocrine factors expression on EC and as such modulates EC properties. Further studies on the importance of miR-363-5p on normal BM function and in disease are warranted.

Treatment, risk factors, and outcome of adults with relapsed AML after reduced intensity conditioning for allogeneic stem cell transplantation

Because information on management and outcome of AML relapse after allogeneic hematopoietic stem cell transplantation (HSCT) with reduced intensity conditioning (RIC) is scarce, a retrospective registry study was performed by the Acute Leukemia Working Party of EBMT. Among 2815 RIC transplants performed for AML in complete remission (CR) between 1999 and 2008, cumulative incidence of relapse was 32% ± 1%. Relapsed patients (263) were included into a detailed analysis of risk factors for overall survival (OS) and building of a prognostic score. CR was reinduced in 32%; remission duration after transplantation was the only prognostic factor for response (P = .003). Estimated 2-year OS from relapse was 14%, thereby resembling results of AML relapse after standard conditioning. Among variables available at the time of relapse, remission after HSCT > 5 months (hazard ratio [HR] = 0.50, 95% confidence interval [CI], 0.37-0.67, P < .001), bone marrow blasts less than 27% (HR = 0.53, 95% CI, 0.40-0.72, P < .001), and absence of acute GVHD after HSCT (HR = 0.67, 95% CI, 0.49-0.93, P = .017) were associated with better OS. Based on these factors, 3 prognostic groups could be discriminated, showing OS of 32% ± 7%, 19% ± 4%, and 4% ± 2% at 2 years (P < .0001). Long-term survival was achieved almost exclusively after successful induction of CR by cytoreductive therapy, followed either by donor lymphocyte infusion or second HSCT for consolidation.

Therapeutic efficacy of polyclonal tregs does not require rapamycin in a low-dose irradiation bone marrow transplantation model

BACKGROUND

Mixed chimerism is an effective strategy for the induction of transplantation tolerance but the toxicity of recipient conditioning makes current bone marrow (BM) transplantation (BMT) protocols unsuitable for widespread clinical application. Therapies promoting BM engraftment under minimal conditioning would facilitate translation of this concept to the clinic. Recently, we have shown that regulatory T cell (Treg) therapy has potent engraftment-enhancing effects in an irradiation-free noncytotoxic BMT protocol, but only if it is combined with rapamycin treatment.

METHODS

Here, we investigated whether polyclonal Treg therapy is effective in promoting chimerism and tolerance in an otherwise unsuccessful BMT protocol using low-dose total body irradiation (1 Gy) and costimulation blockade and determined whether Tregs do so on their own without rapamycin.

RESULTS

The application of polyclonal FoxP3-transduced recipient Tregs led to durable multilineage chimerism and donor-specific skin graft tolerance whereas recipients receiving costimulation blockade alone or green flourescent protein (GFP)-transduced cells failed to develop chimerism. Infused Tregs had a limited life span as indicated by polymerase chain reaction analysis but rather contribute to de novo induction of subsequent Treg generations. Deletion of donor-reactive T cells was observed but progressed more slowly over time compared with recipients of a nonmyeloablative BMT protocol using 3 Gy total body irradiation.

CONCLUSIONS

In conclusion, Treg therapy promotes BM engraftment on its own in a low-dose irradiation BMT protocol, leading to chimerism and tolerance maintained through deletional and nondeletional mechanisms.

New insights in the management of elderly patients with acute myeloid leukemia

PURPOSE OF REVIEW

The management of elderly patients with acute myeloid leukaemia (AML) is more than ever a challenge. Results associated with intensive chemotherapy remain disappointing, at least in nonselected patients. On the contrary, there are still no real standard alternatives even if some new approaches seem promising.

RECENT FINDINGS

Recent studies aim to guide the selection of patients likely to benefit from intensive chemotherapy; to optimize remission induction and maintenance in those patients; and to evaluate long-term results associated with alternative therapies. Main results are the following: favorable AML subsets identified in younger patients remain favorable in elderly patients and might benefit from a relatively intensified treatment; if daunorubicin is used for induction, a dose higher than 45 mg/m2 x 3 results in a higher complete remission rate and longer survival, at least until 65 years of age; repeated intensive postremission courses do not seem to be effective in older patients; and median survival observed after clofarabine or azacitidine-based therapy could be long enough to deserve prospective comparisons against conventional chemotherapy.

SUMMARY

These new results may help to offer a personalized management to elderly patients with AML and to design future trials.