Microvolume fluorimetry for the determination of absolute CD4 and CD8 lymphocyte counts in patients with HIV: a comparative evaluation

Evaluation of a single-platform microcapillary flow cytometer for enumeration of absolute CD4+ T-lymphocyte counts in HIV-1 infected Thai patients

BACKGROUND

Various assays are used to enumerate peripheral blood absolute CD4+ T-lymphocytes. Flow cytometry is considered the gold standard for this purpose. However, the high cost of available flow cytometers and monoclonal antibody reagents make it difficult to implement such methods in the resource-poor settings. In this study, we evaluated a cheaper, recently developed single-platform microcapillary cytometer for CD4+ T-lymphocyte enumeration, the personal cell analyzer (PCA), from Guava Technologies.

METHODS

CD4+ and CD8+ T-lymphocyte counts in whole blood samples from 250 HIV-1 infected Thais were determined, using a two-color reagent kit and the Guava PCA, and compared with the results obtained with two reference microbead-based methods from Becton Dickinson Biosciences: the three-color TruCOUNT tube method and the two-color FACSCount method. Statistical correlations and agreements were determined using linear correlation and Bland-Altman analysis.

RESULTS

Absolute CD4+ T-lymphocyte counts obtained using the Guava PCA method highly correlated with those obtained using TruCOUNT method (R(2) = 0.95, mean bias +13.1 cells/microl, limit of agreement [LOA]-117.9 to +144.1 cells/microl) and the FACSCount method (R2 = 0.94, mean bias = +33.2 cells/microl, LOA-101.8 to +168.3 cells/microl). Absolute CD8+ T-lymphocyte counts obtained using the Guava PCA method also highly correlated with those obtained with the two reference methods (R(2) = 0.92 and 0.88, respectively).

CONCLUSION

This study shows that the enumeration of CD4+ T-lymphocytes using the Guava microcapillary cytometer PCA method performed well when compared with the two reference bead-based methods. However, like the two reference methods, this new method needs substantial technical expertise.

Monitoring antiretroviral therapy in HIV/AIDS patients in resource-limited settings: CD4 counts or total lymphocyte counts?

OBJECTIVE

In order to improve the monitoring of disease progression and therapeutic effectiveness in the management of HIV/AIDS in a resource-limited setting, this study was carried out to establish a correlation between total lymphocyte counts (TLC) and CD4 lymphocyte counts in HIV-1 infected/AIDS adults in Yaoundé, Cameroon.

METHODS

Full blood counts, differential white, and CD4 counts were measured in 149 patients using standard methods. The correlation coefficient established correlation between values. Sensitivity, specificity, and positive predictive values were calculated as required.

RESULTS

The mean TLC, CD4 count, and CD4% as well as CD4/CD8 ratios were 1.932+/-0.895 x 10(9)/L, 268+/-183 cells/mm(3), 14.51+/-15.9%, and 0.34+/-0.25, respectively. Only a weak correlation was observed between TLC and CD4 counts (r=0.41, p=0.05). As a predictor of CD4 count, TLC cut-offs <2.0 and <1.0 x 10(9)/L were unable to predict these values reliably, but showed that at TLC cut-offs of <1.0 x 10(9)/L there was a high chance of CD4 counts being under 200 cells/mm(3).

CONCLUSIONS

These data suggest that TLC are of limited value in predicting CD4 counts and should not be substituted for CD4 counts whenever possible. However, TLC may be reliably used in designing algorithms and programs for initiating patient management and follow-up in this setting.

Evaluation of a new single-parameter volumetric flow cytometer (CyFlow(green)) for enumeration of absolute CD4+ T lymphocytes in human immunodeficiency virus type 1-infected Thai patients

Use of the standard dual-platform flow cytometric method for determination of CD4(+) T-lymphocyte counts, which needs both a flow cytometer (FCM) and hematological analyzer, would inevitably lead to increased variability. The development of new single-platform (SP) FCMs that provide direct CD4(+) T-lymphocyte counts for improved assay precision and accuracy have recently attracted attention. This study evaluated one of those systems, CyFlow(green) (Partec), a single-parameter SP volumetric FCM. The performance of CyFlow(green) was compared with those of two reference standard SP microbead-based technologies of the three-color TruCOUNT tube with the FACScan FCM and a two-color FACSCount system (Becton Dickinson Biosciences). Absolute CD4(+) and CD8(+) T-lymphocyte counts in 200 human immunodeficiency virus type 1-seropositive blood specimens were determined. Statistical analysis for correlation and agreement were performed. A high correlation of absolute CD4 counts was shown when those obtained with CyFlow(green) were compared with those obtained with the bead-based three-color TruCOUNT system (R(2)=0.96; mean bias, -69.1 cells/microl; 95% confidence interval [CI], -225.7 to+87.5 cells/microl) and the FACSCount system (R(2)=0.97; mean bias, -40.0 cells/microl; 95% CI, -165.1 to+85.1 cells/microl). The correlation of the CD4(+) T-lymphocyte counts obtained by the two bead-based systems was high (R(2)=0.98). Interestingly, CyFlow(green) yielded CD4(+) T-lymphocyte counts that were 21.8 and 7.2 cells/microl lower than those obtained with the TruCOUNT and the FACSCount systems, respectively, when CD4(+) T-lymphocyte counts were <250 CD4(+) T-lymphocyte counts/microl range or 17.3 and 5.8 cells/microl less, respectively, when CD4(+) T-lymphocyte counts were <200 cells/microl. The single-parameter CyFlow(green) volumetric technology performed well in comparison with the performance of the standard SP bead-based FCM system. However, a multicenter comparative study is needed before this FCM machine is implemented in resource-limited settings.

Perfect count: a novel approach for the single platform enumeration of absolute CD4+ T-lymphocytes

BACKGROUND

The derivation of reliable CD4(+) T lymphocyte counts is vital for the monitoring of disease progression and therapeutic effectiveness in HIV(+) individuals. Flow cytometry has emerged as the method of choice for CD4(+) T lymphocyte enumeration, with single-platform technology, coupled with reference counting beads, fast becoming the "gold standard." However, although single-platform, bead-based, sample acquisition requires the ratio of beads to cells to remain unchanged, there is no available method, until recently, to monitor this.

METHODS

Perfect Count beads have been developed to address this issue and to incorporate two bead populations, with different densities, to allow the detection of inadequate mixing. Comparison of the relative proportions of both beads with the manufacture's defined limits enables an internal QC check during sample acquisition. In this study, we have compared CD4(+) T lymphocyte counts, obtained from 104 HIV(+) patients, using TruCount beads with MultiSet software (defined as the predicated method) and the new Perfect Count beads, incorporating an in house sequential gating strategy.

RESULTS

We have demonstrated an excellent degree of correlation between the predicate method and the Perfect Count system (r(2) = 0.9955; Bland Altman bias +27 CD4(+) T lymphocytes/microl).

CONCLUSIONS

The Perfect Count system is a robust method for performing single platform absolute counts and has the added advantage of having internal QC checks. Such an approach enables the operator to identify potential problems during sample preparation, acquisition and analysis.

Simplified Volumetric Flow Cytometry Allows Feasible and Accurate Determination of Cd4 T Lymphocytes in Immunodeficient Patients Worldwide

The determination of CD4 cells is of crucial clinical importance for patients with AIDS. However, the high costs involved represent limitations for CD4 cell counting in developing countries. In order to provide an affordable technique, we introduced a simplified volumetric counting (SVC) technique without sample manipulations and investigated it in a multicentre study. Blood samples from 434 healthy donors and immunodeficient patients were tested in eight hospital laboratories in Europe, Africa and Asia. CD4 cell counts were compared using inhouse flow cytometric methods and the SVC technique. The SVC method was performed on a low-cost flow cytometer (CyFlow SL, Partec, Münster, Germany) after 15 min antibody incubation without pre-analytic manipulations, such as washing or erythrocyte lysing procedures. Linear regression analysis demonstrated a correlation of r=0.942 (Europe), r=0.952 (Africa) and r=0.989 (Asia) between the SVC technique and the in-house methods. Bland Altman plot analysis of all patient data showed a mean bias between the two methods of +26 CD4 cells in favour of the SVC technique (measured range: 6–1905 cells/μl; median CD4 cell count: 388/μl). Three centres used the FACS-count technique (Becton-Dickinson, San José, Calif., USA) as an in-house method dispensing with pre-analytic manipulations. The comparison of SVC and FACS-count method revealed a mean bias of +32 CD4 cells/μl (median CD4 cell count: 349/μl). The accuracy of the SVC was tested on standards with known CD4 cell counts ( n=6) and was shown to be 95.2%. The low-cost device and the simplified no-lyse, no-wash test procedure reduces the costs per determination and facilitates the use of flow cytometry in developing countries.

Precise CD4 T-cell counting using red diode laser excitation: for richer, for poorer

BACKGROUND

Measuring CD4 T-cell counts at low cost is relevant in dealing with the human immunodeficiency virus (HIV) epidemic throughout the developing world. The recently introduced novel concepts in gating strategies and sample stabilization facilitate affordable immunophenotyping by flow cytometry. However, the impact of these developments is still limited by the high cost of currently available flow cytometers.

METHODS

Diode lasers emitting 10-15 mW at 635 nm are one-tenth the size and cost and require one thousandth the power of an equivalent 488-nm argon ion laser. We used the available 635-nm diode-based flow cytometers, including PA-II, Luminex 100, SuperMot, and FACSCalibur, to investigate whether these instruments can generate reliable CD4 counts when used with allophycocyanin (APC) and cyanin-5 (Cy5)-labeled CD4 antibodies.

RESULTS

We document the feasibility of obtaining leucocyte differential counts using orthogonal side scatter (SSC) without the need for forward scatter (FSC). Accurate CD4% values among lymphocytes and leucocytes can be obtained by primary CD4 gating using a single CD4 monoclonal antibody conjugated to APC or Cy5. Double immunofluorescence (IF) staining with CD4-APC (FL1) and CD45-APC-Cy7 (FL2) introduces pan-leucogating for a convenient assessment of absolute CD4 counts on double platforms. We demonstrate that small flow cytometers with laser diodes are capable of delivering absolute CD4 T-cell counts with a precision similar to the performance of the current state-of-the-art single-platform instruments (e.g., the CytoronAbsolute; R(2) = 0.961). In this respect, they appear to be superior to the nonflow CD4 counting techniques.

CONCLUSIONS

Accurate CD4 counts can be generated at minimal cost on red diode laser-operated flow cytometers, retaining the potential for high throughput capacity without compromising precision. With further improvements in volumetric technology and clinical software, these cytometers may develop into a new generation of inexpensive battery-operated laboratory hardware that combines cellular phenotyping with bead-based multiplexing immunoassays for (HIV) serology.

CD45-assisted PanLeucogating for accurate, cost-effective dual-platform CD4+ T-cell enumeration

BACKGROUND

North American and European guidelines for dual-platform (DP) flow cytometry recommend absolute CD4 T-cell counts to be calculated from two parameters: the absolute lymphocyte counts obtained on a hematology analyzer and the percentages of CD4+ cells among lymphocytes (CD4%/lympho) obtained by flow cytometry. Nevertheless, the identification of lymphocytes is error-prone: a poor match between these common denominators in the two systems is the main source of inaccuracy. In contrast, total leucocyte counts (white cell counts [WCC]) and CD4% among the gated CD45+ leucocytes (CD4%/leuco) can be determined with greater accuracy.

METHODS

We introduced "PanLeucogating," i.e., we used total leucocytes as the common denominator for improving the precision of DP absolute CD4 counting. Correlations and Bland-Altman tests were used for statistical analysis.

RESULTS

First, 22 stabilized blood product samples were provided by U.K. National External Quality Assessment Scheme (NEQAS) and a higher accuracy and precision of CD4 counts were documented using PanLeucogating compared with lymphocyte gating. Next, 183 fresh and 112 fixed (TransFix) whole blood samples were used to compare DP methods and single-platform (SP) methodology, including both volumetric and bead-based techniques. A particularly high correlation and comparable precision of absolute CD4 counts were observed between the SP volumetric method and DP PanLeucogating (R(2) = 0.990; bias 6 +/- SD 17%). The SP volumetric method showed lower levels of agreement with the DP lymphocyte gating (R(2) = 0.758; bias 14 +/- SD 51%) and with the SP bead-based method (R(2) = 0.923; bias 4 +/-SD 31%).

CONCLUSIONS

These observations show that DP leucocyte counts (WCC) should replace lymphocyte counts as the "common denominator" although CD4%/lympho values can, as an extra step, be also provided readily if requested. When coupled with quality control for WCC on hematology analyzers, the DP method with CD45 PanLeucogating represents a robust CD4 T-cell assay that is as accurate as the SP volumetric technique. This DP method uses only two, CD45 and CD4, antibody reagents and can be run on any pair of hematological analyzer plus flow cytometer.