Reduced Intensity Conditioning With Clofarabine, Antithymocyte Globulin (ATG), Total Lymphoid Irradiation (TLI) Followed by Allogeneic Stem Cell Transplant

One approach to limit the toxicity of allogeneic transplantation has been the use of
nonmyeloablative regimens preceding the infusion of allogeneic cells.In this strategy,
patients receive immunosuppressive therapy that allows for the engraftment of donor cells
without the immediate eradication of patient hematopoiesis.The primary mechanism by which the
underlying disease is eradicated is not through chemotherapy mediated cytoreduction, but
rather through the donor lymphocyte mediated graft versus tumor effect.As a result, patients
experience far less regimen related toxicity.Therefore, the adoption of this strategy may
allow for the use of allogeneic transplantation in disease settings and patient populations
for which it had not been readily applicable in the past.

Over the past several years, the use nonmyeloablative transplant has rapidly expanded.Several
reduced intensity conditioning regimens have been developed including fludarabine and
cyclophosphamide; fludarabine and melphalan; fludarabine, ATG and low dose busulfan; and
fludarabine and low dose TBI. Investigators have demonstrated the feasibility of this
treatment approach with the majority of patients demonstrating donor engraftment,decreased
regimen related toxicity, and graft mediated regression of disease.In some studies, patients
demonstrate a period of mixed donor/host chimerism in which the infusion of donor lymphocytes
is associated with achievement of complete donor chimerism.

Although regimen related toxicity is decreased following reduced intensive conditioning
regimens, graft versus host disease and opportunistic infections remain a significant source
of morbidity and mortality following nonmyeloablative allogeneic transplantation. The impact
of nonmyeloablative transplantation on immunological reconstitution has not been fully
defined. Persistence of host antigen presenting cells in the post-transplant period may
increase the incidence of GVHD due to the presentation of alloantigens to donor T cells. In
contrast, residual host cellular immunity may provide enhanced protection against infectious
pathogens and allow for more rapid education of donor lymphocytes.

The use of clofarabine in place of fludarabine in combination with cyclophosphamide may
augment the anti-leukemia effect of the regimen, enhance cytoreduction, and increase the
efficacy of reduced intensity allogeneic transplantation in this setting.A potential issue
associated with the use of clofarabine and cyclophosphamide as pre-transplant conditioning is
whether the regimen would be sufficiently immunosuppressive to reliably facilitate
engraftment of donor hematopoiesis.Another concern relates to the significant incidence of
graft versus host disease which remains a major source of morbidity and mortality following
reduced intensity transplantation.The use of TLI and ATG has been studied in the context of
allogeneic transplantation and has been shown to effectively support engraftment in animal
models and clinical trials.TLI has been shown to promote immune tolerance resulting in a
decrease in the incidence of graft versus host disease (GVHD).It has been shown to decrease
the incidence of rejection following transplantation of a T cell depleted allograft.The
conditioning regimen of TLI and cyclophosphamide results in successful engraftment in
patients with aplastic anemia.

Regulatory T cells represent a population of T lymphocytes that demonstrate an
immunosuppressive phenotype and play an important role in the prevention of autoimmunity and
transplant rejection.Regulatory cells express the inhibitory cytokines IL-10 and TGFβ and are
thought to suppress immune activation through direct cell contact.Similar to activated
effector cells they coexpress CD4 and CD25.Regulatory T cells may be identified by the high
levels of CD25 expression and the presence of CTLA-4 and FOXP3.Regulatory T cells demonstrate
minimal proliferation to allogeneic stimuli and inhibit third party mixed lymphocyte
responses. Increased presence of regulatory T cells have been found in the tumor bed,
draining lymph nodes, and circulation in patients with malignancy and inhibit host anti-tumor
immune responses.

There has been increasing interest in evaluating the role of regulatory T cells as a means of
inhibiting graft versus host disease. In animal models, selective introduction of regulatory
T cells prevents the development of graft versus host disease without compromising immune
reconstitution or anti-tumor immunity. A variety of strategies for the ex vivo expansion and
isolation of regulatory T cells have been explored. A limiting factor has been the similar
patterns of expression of cell surface markers between regulatory and activated T cell
populations. iNKT cells represent another population of immunomodulatory cells thought to be
essential for the generation of tolerance.In pre-clinical models, TLI has been shown to
modulate immune effector cells resulting in increased levels of circulating regulatory T
cells, preventing GVHD in a mismatched transplant setting.It is thought that iNKT cells are
selectively preserved after TLI which polarize T cells towards an inhibitory phenotype. In a
clinical study, 37 patients with lymphoid malignancies or acute leukemia underwent
conditioning with TLI administered as 10 fractions of 80cGy and ATG.Only 2 patients developed
acute GVHD despite the observation of a graft versus disease effect.Of note, a significant
increase in the number of donor CD4+ T cells expressing IL-4 was observed suggesting that the
immune modulation resulting from TLI/ATG polarized cells towards a TH-2 phenotype.As such,
TLI/ATG would like facilitate engraftment and decrease the incidence of GVHD in patients
undergoing conditioning with clofarabine.Most importantly, by modulating the host immune
effectors but not depleting donor T cells, this strategy should not significantly inhibit the
graft versus tumor effect.The prevalence of dendritic cell (DC) subsets (DC1 vs. DC2) in the
hematopoietic graft have also been shown to effect the risk of GVHD.

Inclusion Criteria:

1. Patients with a)acute myeloid leukemia exclusive of patients in first complete
remission with good risk cytogenetics (translocation 8,21,translocation 15, 17 or
inversion 16); B)myelodysplastic syndrome; c)acute lymphocytic leukemia exclusive of
patients in first remission without negative prognostic markers; d) relapsed or
refractory nonHodgkin's lymphoma or Hodgkin's disease; e)relapsed or refractory
multiple myeloma or f)relapsed or refractory chronic lymphocytic leukemia.

2. Patients who are considered appropriate for reduced intensity transplantation must
present with at least one of the following: A. Age over 50 B. History of a prior
hematopoietic stem cell transplant C. Patient with compromised organ function or
comorbid conditioning such that a standard ablative transplant would be considered
high risk. D. Patient with low grade Lymphoma or CLL for which reduced intensity
transplant would be the optimal therapy compared to an ablative regimen

3. Patients will have a related or unrelated donor matched at 5/6 or 6/6 HLA loci.

4. Patients must be greater than or equal to 18 years old, and younger than or equal to
75 years old to participate in the study.

5. Patients must have ECOG performance status of 0-2

6. Pulmonary function tests demonstrate DLCO (adjusted for Hgb)>50% predicted

7. Cardiac ejection fraction >40%

8. Laboratories:

- Bilirubin less than or equal to 1.5mg/dL x ULN

- AST/ALT/Alkaline Phosphatase less than or equal to 2.5x ULN

- Serum creatinine less than or equal to 1.0mg/dL; if serum creatinine > 1.0MG/dL,
then the estimated glomerular filtration rate (GFR) must be >60mL/min/1.73m^2 as
calculated by the Modification of Diet in Renal Disease equation where Predicted
GRF (ml/min/1.73m^2)=186x (serum creatinine)^1.154x(age in years)^-0.203x(0.742
if patient is female) x (1.212 if patient is black)

9. Patients with serologic evidence of hepatitis B or C exposure will undergo liver
biopsy to assess for presence of active hepatitis or fibrosis and quantification of
risk of proceeding with transplant.

10. All patients must be capable of understanding the investigational nature, potential
risks and benefits of the study, and able to provide valid informed consent. All patients
must be informed of the investigational nature of this study and must give written informed
consent in accordance with institutional and federal guidelines.

11. Female patients of childbearing potential must have a negative serum pregnancy test
within 2 weeks prior to enrollment.

12. Male and female patients must use an effective contraceptive method during the study
and for a minimum of 6 months after study treatment

Exclusion Criteria:

1. Patients who are HIV+ will be excluded.

2. Patients must not have serious intercurrent illness such as uncontrolled systemic
infection or significant organ compromise which significantly increases the risk of
undergoing allogeneic transplantation.

3. Pregnant and lactating women will be excluded.