Patients with active acute leukemia have dismal prognoses even with allogeneic transplantation.Thus,new measures to enhance graft versus leukemia effect and reduce relapse rates are needed.

Relapse risk after double umbilical cord transplantations have been shown to be significantly lower compared to matched sibling and matched unrelated donor transplantations due to better graft versus leukemia effect.

The investigators hypothesize, that concomitant transplantation from 2 matched siblings may improve GVL effect and reduce relapse rate in patients with high risk acute leukemias and other high risk hematological malignancies.

Inclusion Criteria:

1. Age 18 years or older

2. Patients with refractory or relapsed acute leukemia unable to receive myeloablative conditioning.

3. Patients with refractory or relapsed acute leukemia able to receive myeloablative conditioning but with the following factors:

   AML- 2 or more of the following: duration of CR1 < 6 months, poor cytogenetics, circulating blasts, karnofsky < 90.

   ALL- age > 40 or second and additional relapse, or 2 or more of the following: BM blasts > 25%, age 18-39,first refractory relapse, donor CMV positive.

4. Patients with 2 matched siblings and donor age > 18 years old.

5. Patients with advanced multiple myeloma with life expectancy of less than 6 months with standard therapy or transplantation.

6. Patients with advanced lymphoma with life expectancy of less than 6 months with standard therapy or transplantation.

Exclusion Criteria:

1. Patient age < 18 years.
2. Donor age < 18 years.
3. Patients in remission or not fulfilling above disease criteria -