Table 3.
Different methods for generation of VST
| I. In vitro stimulation and expansion of VST [80,86,95,96] |
|
|
| • Repeated stimulation of donor derived peripheral blood mononuclear cells with antigen presenting cells (APC) pulsed with target antigens. Ultimately expansion of T cells using IL-2. |
| • Various antigen presenting cells include dendritic cells, monocytes, PHA blasts, B cells and artificial APC can be utilized. |
| • Antigen sources are comprised of whole virus/viral lysate, whole proteins, viral vectors and peptide/peptide mixtures. |
| • Advantage and disadvantage: |
| ◦ It is the first and most commonly used protocol. |
| ◦ Need relatively a small volume of blood. |
| ◦ Final product containing polyclonal T cells. |
| ◦ This method require a long production time. |
|
|
| II. Direct selection of VST [80,86,95,96] |
|
|
| • Donor white blood cells are isolated in vitro via three different method: |
| - Peptide-HLA multimers. |
| - Cytokine-capture method after exposure to viral antigen. |
| - Based on expression and upregulation of activation molecules on the cell surface such as CD137 (4-1BB) and CD154 (CD40L). |
| • Advantage and disadvantage: |
| ◦ It is a more rapid way to generate VST. |
| ◦ This technique is basically limited to donors with specific immunological memory T cells for the virus. |
| ◦ Large volume of donor blood (100-500 mL) is typically required to reach valuable cell doses. |
| ◦ In vitro activation or expansion lead to exhaustion of T cells. |
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|
| III. Multivirus-specific T cells [80,86,95,96] |
|
|
| • Generation of VST for each single virus need a separate manufacturing process and it is time and cost consuming. Different practices for the generation of multivirus-specific T cells in one single step have been established. |
| • This product can be used for patients with multiple refractory viral infections. |
| • Advantage and disadvantage: |
| ◦ Targeting of various viruses in a solitary product. |
| ◦ Challenges comprise production time, cost, and labor. |
| ◦ A potential difficulty is that the most immunodominant antigens will prevent other T cell expansions and diminish the final product of clonal diversity. |
|
|
| IV. Third Party VST [80,86,95] |
|
|
| • Manufacturing of donor-derived VST is not always conceivable because of virus seronegative donors or patients undergoing umbilical cord blood (UCB) transplantation. Third-party VST can be utilize for these patients. |
| • Third-party VST represent an alternative option in patients who don’t respond to donor-derived VST because of mutations in viral genome that cannot be recognized by donor T cells. |
| • This product derived from unmatched donors. |
| • Advantage and disadvantage: |
| ◦ Since it is not from autologous or HLA-matched sources, may increase the risk of GVHD. |
| ◦ It is a partially matched product that could be recognized by the host immune system leading to rejection of VST. |
| ◦ It is a products that could be immediately available in the patients with refractory infections. |
| ◦ It is for “off the shelf” administration that lead to avoid any risky delay in the management of viral disease. |