Fc receptors and human T lymphocytes in frozen-thawed peripheral blood cells

A flow cytometric method to assess antigen-specific proliferative responses of different subpopulations of fresh and cryopreserved human peripheral blood mononuclear cells

We have used PKH26 dye, which is incorporated stably into the membrane of cells, to determine, using flow cytometry, lymphocyte proliferative responses to the antigen tetanus toxoid in fresh and cryopreserved samples. Measuring cell proliferation with this dye has advantages over either 3H-thymidine or Bromodeoxyuridine (BrdU). Whereas the existing methods measure proliferation at a single time point, PKH26 gives a cumulative measure of cell proliferation. As PKH26 is incorporated into the cell membrane, cells do not have to be permeabilised to allow dye incorporation into a cytoplasmic compartment. Most importantly, PKH26 can be used in combination with monoclonal antibodies to surface markers on mixed populations of cells, to determine the proliferation of individual subpopulations, without the need for prior cell fractionation. We also show that PKH26 can be used with similar efficacy in both fresh and cryopreserved samples. In addition since PKH26 is a cumulative measure of proliferative responses we were able to show that restimulation of the dividing population in vitro with fresh antigen presenting cells (APC) and antigen permits characterisation of a further proliferating cell population. The use of PKH26 dye in combination with cell phenotyping and measurement of cytokine production at the single cell level will prove a powerful tool for multiparameter analyses of cellular responses to antigen.

Comparative evaluation of fresh, fixed, and cryopreserved solid tumor cells for reliable flow cytometry of DNA and tumor associated antigen

Five different protocols for the short-term preservation of cells used for multiparameter flow cytometric assay of tumour associated antigens (TAA) and DNA were assessed in cell suspensions prepared by mechanical disaggregation of 15 gynecological tumors. The protocols at 4 degrees C were 1) storage in buffer, 2) storage in 50% methanol, and 3) storage in buffer after formalin fixation. Tissues were also cryopreserved as cell suspensions and tissue blocks. When the TAA expression and DNA histograms of the preserved cells were compared with those in fresh cell suspensions, cryopreservation was found to be the best method: TAA expression was well preserved and there was a good correlation between TAA expression and the quality of the DNA histograms, respectively, in fresh and cryopreserved cells (RS: 0.82-0.91, P less than 0.001 for all TAAs). The cell suspensions preserved at 4 degrees C all showed a significant increase in background fluorescence (P less than 0.05) and a reduction in the TAA specific fluorescence (P less than 0.011). Methanol fixation was better than buffered formalin for the proteins studied, though both gave significantly worse results than cryopreservation. The quality of these cell suspensions and the correlation with TAA measurements in fresh cell suspensions deteriorated progressively with time, particularly if they were stored more than a week.

Non-random cell killing in cryopreservation: implications for performance of the battery of leukocyte tests (BLT), I. Toxic and immunotoxic effects

To eliminate between-tests error in longitudinal human studies, for specimen sharing, convenient scheduling, etc., it is necessary for us to freeze leukocytes as well as non-transformed, continuous T lymphocyte (CTL) lines. Two commonly used cryopreservation methods were compared in terms of efficacy. Isolated peripheral blood mononuclear cells and CTLs were each aliquoted into three sets of vials. Two sets each were frozen in a 1:1 mixture of 15% DMSO in Mixed Medium (MM) and 20% FBS in MM using a commonly employed styrofoam freezer insert method for liquid nitrogen refrigerators and a programmed freezer (temperature falls at an optimal rate), respectively. The remaining set was held in MM with 20% FBS at 20 degrees C during the 2-h freezing process. The cells were thawed and/or washed and assayed for viability and T helper (Th)/T suppressor (Ts) ratio. It is clear that inadequate freezing (via the styrofoam method) non-randomly damages cells of T cell subpopulations, Th being more sensitive than Ts. Further, it is shown that inadequate cryopreservation can confound results from a number of assessment methods owing to morphological and functional damages. The battery of leukocyte tests (BLT) under development in this laboratory, is designed to detect toxic, immunotoxic and genotoxic effects of in vivo mutagen exposure on human blood. It is concluded that minimization of non-random cell losses (as quantitated on the basis of morphology) and preservation of related regulatory cell function is essential if one would assess the in vivo and in vitro states of heterogeneous cells. Further, it is suggested that freezing methods should be used only after verification that selective damage to subpopulations is not occurring among cells that otherwise might wrongly be assumed to be intact.

Cryopreservation and short-term storage of human lymphocytes for surface marker analysis. Comparison of three methods

Three methods were compared for the cryopreservation and short-term storage of human lymphocytes for cell surface marker analysis with monoclonal antibodies and flow cytometry. These methods were controlled-rate freezing followed by storage in liquid nitrogen (CR), direct placement into liquid nitrogen (LN), and direct placement at -70 degrees C (-70). Our findings show that the LN and -70 methods of cryopreserving lymphocytes are as effective as the CR method for the purpose of determining T cell and large granular lymphocyte subsets within 1 month after freezing.

Susceptibility of human T cells, T-cell subsets, and B cells to cryopreservation

We have studied the number of viable and functionally active T and B lymphocytes obtainable after cryopreservation to determine the best and most practical way to recover the maximal number of viable and functionally active cells. Assays were done on purified populations of human T and B cells recovered after cryopreservation. The results were compared to those obtained from similar types of cells fractionated from fresh and from cryopreserved mononuclear cells. The number of viable T cells recovered after cryopreservation was significantly lower than the number of viable T cells obtained from either fresh or cryopreserved mononuclear cells. The residual viable T cells recovered after cryopreservation showed significantly reduced blastogenic activity in response to pokeweed mitogen (PWM) stimulation. This occurred despite their normal blastogenic response to phytohemagglutinin and their normal ability to help B cells in the production of immunoglobulins following PWM stimulation. The reduction in the blastogenic responses of these T cells to PWM stimulation is attributed to the loss of a portion of the PWM responding subset of T cells. The loss in this subset of T cells was related to the exposure of cells to ammonium chloride prior to cryopreservation. The viability and functional abilities of B cells were not affected regardless of whether purification was done before or after cryopreservation. These findings indicate that extrinsic membrane damage to T cells induced prior to cryopreservation can affect the viability and responsiveness of a certain population of normal T cells. The damage can be minimized by reversing the sequence of T-cell isolation and freezing so that isolation of T cells is done after, rather than before, freezing. These results could be important in the study of T cells from patients with T-cell abnormalities, since the patients' cells could have an intrinsic membrane defect which would make them sensitive to freezing similar to that induced by extrinsic damage.