Frequently Asked Questions

Stem Cells Overview

There are three main properties that make stem cells different from other cells:

  • Stem cells are unspecialized and do not possess tissue-specific characteristics to perform specialized functions.
  • Through differentiation, stem cells can become specialized to produce tissue-specific cells, e.g., red blood cells or kidney cells.
  • Stem Cells are self-sustaining and can divide for much longer periods of time than, for example, skin cells.

Cell potency means the relative flexibility of stem cells to differentiate into specialized cells. Stem cells with greater potency can generate more cell types than those with lower potency.

Hierarchy of Cell Potency

  • Totipotent stem cells can produce any cell type in the body.
  • Pluripotent stem cells can give rise to all cell types except the placenta.
  • Multipotent stem cells can develop a more limited number of cell types.

A bone marrow transplant is a medical procedure in which healthy blood-forming hematopoietic stem cells are infused into a patient to replace bone marrow that may have been damaged or destroyed by disease, infection, or chemotherapy. These stem cells travel to the bone marrow (soft, sponge-like tissue in the center of most bones) where they produce new blood cells and promote growth of new marrow. A bone marrow transplant is also called a stem cell transplant.

Hematopoietic Stem Cells

An immature cell that can develop into all types of blood cells, including white blood cells, red blood cells, and platelets.

Hematologic malignancies are cancers that affect the body’s blood, bone marrow, or lymphatic systems. They are the fifth most commonly occurring cancers and the second leading cause of cancer death. The most common forms of hematologic cancers include leukemia, lymphoma, and multiple myeloma.

After HSCs are collected, the patient undergoes chemotherapy and/or radiation to destroy cancer cells, thus creating space in the bone marrow for new healthy cells. The harvested bone marrow or blood stem cells are given to the patient using a flexible tube inserted into a vein. These cells migrate to the bone marrow, proliferate and differentiate resulting in the production of normal, mature blood cells.

Yes, HSC transplantation has been in medical practice for 70 years. Tens of thousands of procedures are conducted annually in the U.S. for patients with blood cancers and other severe conditions. Despite this success, significant numbers of these patients suffer serious, lifelong adverse events, such as graft vs. host disease (GVHD), or fail to receive the treatment because they cannot be matched to a suitable donor for a transplant.

HSCs can be sourced from umbilical cord blood (CB), peripheral blood, or bone marrow. Advantages to the use of CB-sourced HSCs include low graft vs. host disease (GvHD), increased graft vs. tumor effect, and donor matching. Disadvantages have traditionally been low cell number, long engraftment time, and higher cost.

We use a simple low-cost manufacturing process that overcomes the limitations of traditional CB transplants, namely low cell numbers, poor engraftment efficiency, and infection.


Megakaryocytes are specialized cells that originate from hematopoietic stem cells (HSCs) and form platelets, which are involved in clotting.

Thrombocytopenia is a medical condition that occurs when a patient does not have enough platelets in his or her blood, resulting in a high risk for bleeding. Thrombocytopenia can be inherited or can be caused as a result of several conditions or medications. Circulating platelets can be reduced by decreased platelet production, increased destruction, or being trapped in the spleen. Sometimes a drug confuses the immune system and makes it destroy platelets. Examples include heparin, quinine, sulfa-containing antibiotics, and anticonvulsants.

Current medical procedures call for dosing patients repeatedly with units of fresh platelets derived from voluntary donors. In contrast, Tacitus Therapeutics’ MEG100 technology is a one-time infusion expected to produce platelets in the patient’s own body naturally. Megakaryocyte cells are eventually cleared by the body (i.e. they don’t engraft permanently like hematopoietic stem cells (HSCs)).

Because platelets typically cannot be cryopreserved, shortages and logistical supply problems arise. However, Tacitus Therapeutics’ technology enables megakaryocytes cryopreservation, long-term storage, and curative potential.

Therapeutic benefit of megakaryocyte infusion has not yet been established, however, platelet transfusion has been in medical practice for 70 years and is considered among the most effective and safest medicines. Millions of platelet units are transfused annually in the U.S. The majority are used for patients with blood cancers or other hematological disorders to prevent bleeding during chemotherapy or stem cell transplants. However, platelets have a limited shelf-life of 10 days, which necessitates developing a complex infrastructure to collect and deliver this type of therapy to support the need for repeat transfusions. Infusion of megakaryocytes has the potential to overcome these limitations of platelet therapy.

Tacitus Therapeutics’ MEG100  is a cryopreserved off the shelf product with the potential to produce platelets naturally within the patients’ own body.  This alleviates major limitations of platelet therapies, namely that the poor stability of platelets necessitates a large supply chain of volunteer donors or complex approaches to on-demand manufacture using bioreactors. This, in turn, creates additional safety risks associated with infectious pathogens and alloimmunization.

Clinical Trials

Yes, Tacitus Therapeutics is currently conducting a clinical trial to evaluate the safety of HSC100 in patients with refractory hematological malignancies undergoing allogeneic transplantation.  

HSC100 is an investigational therapy based on allogeneic hematopoietic stem cells (HSCs) expanded from umbilical cord blood. HSC100 is being investigated currently in an open-label Phase I clinical trial in the United States1 for treatment of hematological malignancies. For more information on HSC100 clinical trials, please visit identifier NCT03885947.