CD4+ cell-dependent granuloma formation in humanized mice infected with mycobacteria.

We have used humanized mice, in which human immune cells differentiate de novo from transplanted cord blood progenitor cells, to study the human immune responses to infection with Mycobacterium bovis bacillus Calmette-Guérin and Mycobacterium tuberculosis. Granulomas with a core containing giant cells, human CD68(+) macrophages, and high bacilli numbers surrounded by a layer of CD3(+) T cells and a fibrotic response encapsulating the lesions were observed in livers and lungs from bacillus Calmette-Guérin-infected humanized mice but not in nonhumanized infected controls. Paradoxically, humanized mice contained higher mycobacterial numbers in organs than nonhumanized controls. The enhancement of bacterial load was mediated by human CD4(+) cells and associated to an increased expression of Programmed Death-1 protein and CD57 on T cells, molecules associated with inhibition and senescence. The lesions from mice depleted of CD4(+) cells were scarcer, minimal, and irregular compared with those from mice depleted of CD8(+) cells or nondepleted controls. Granulomas of bacillus Calmette-Guérin-infected humanized mice administered with a TNF-neutralizing TNF receptor fusion molecule preserved their structure, but contained higher levels of intracellular bacilli. Extended necrosis was observed in granulomas from M. tuberculosis- but not bacillus Calmette-Guérin-infected humanized mice. Our data indicate that humanized mice can be used as a model to study the formation and maintenance of human granuloma in tuberculosis and other infectious or noninfectious diseases.

Silencing suppressor of cytokine signaling-1 (SOCS1) in macrophages improves Mycobacterium tuberculosis control in an interferon-gamma (IFN-gamma)-dependent manner.

Protection against infection with Mycobacterium tuberculosis demands IFN-γ. SOCS1 has been shown to inhibit responses to IFN-γ and might thereby play a central role in the outcome of infection. We found that M. tuberculosis is a highly efficient stimulator of SOCS1 expression in murine and human macrophages and in tissues from infected mice. Surprisingly, SOCS1 reduced responses to IL-12, resulting in an impaired IFN-γ secretion by macrophages that in turn accounted for a deteriorated intracellular mycobacterial control. Despite SOCS1 expression, mycobacteria-infected macrophages responded to exogenously added IFN-γ. SOCS1 attenuated the expression of the majority of genes modulated by M. tuberculosis infection of macrophages. Using a conditional knockdown strategy in mice, we found that SOCS1 expression by macrophages hampered M. tuberculosis clearance early after infection in vivo in an IFN-γ-dependent manner. On the other hand, at later time points, SOCS1 expression by non-macrophage cells protected the host from infection-induced detrimental inflammation.

Nonhematopoietic cells control the outcome of infection with Listeria monocytogenes in a nucleotide oligomerization domain 1-dependent manner.

We analyzed the defensive role of the cytosolic innate recognition receptor nucleotide oligomerization domain 1 (NOD1) during infection with Listeria monocytogenes. Mice lacking NOD1 showed increased susceptibility to systemic intraperitoneal and intravenous infection with high or low doses of L. monocytogenes, as measured by the bacterial load and survival. NOD1 also controlled dissemination of L. monocytogenes into the brain. The increased susceptibility to reinfection of NOD1(-/-) mice was not associated with impaired triggering of listeria-specific T cells, and similar levels of costimulatory molecules or activation of dendritic cells was observed. Higher numbers of F480(+) Gr1(+) inflammatory monocytes and lower numbers of F480(-) Gr1(+) neutrophils were recruited into the peritoneum of infected WT mice than into the peritoneum of infected NOD1(-/-) mice. We determined that nonhematopoietic cells accounted for NOD1-mediated resistance to L. monocytogenes in bone marrow radiation chimeras. The levels of NOD1 mRNA in fibroblasts and bone marrow-derived macrophages (BMM) were upregulated after infection with L. monocytogenes or stimulation with different Toll-like receptor ligands. NOD1(-/-) BMM, astrocytes, and fibroblasts all showed enhanced intracellular growth of L monocytogenes compared to WT controls. Gamma interferon-mediated nitric oxide production and inhibition of L. monocytogenes growth were hampered in NOD1(-/-) BMM. Thus, NOD1 confers nonhematopoietic cell-mediated resistance to infection with L. monocytogenes and controls intracellular bacterial growth in different cell populations in vitro.

Loss of a child and the risk of amyotrophic lateral sclerosis.

Between 1987 and 2005, the authors conducted a case-control study nested within the entire Swedish population to investigate whether loss of a child due to death is associated with the risk of amyotrophic lateral sclerosis (ALS). The study comprised 2,694 incident ALS cases and five controls per case individually matched by year of birth, gender, and parity. Odds ratios and their corresponding 95% confidence intervals for ALS were estimated by using conditional logistic regression models. Compared with that for parents who never lost a child, the overall odds ratio of ALS for bereaved parents was 0.7 (95% confidence interval (CI): 0.6, 0.8) and decreased to 0.4 (95% CI: 0.2, 0.8) 11-15 years after the loss. The risk reduction was also modified by parental age at the time of loss, with the lowest odds ratio of 0.4 (95% CI: 0.2, 0.9) for parents older than age 75 years. Loss of a child due to malignancy appeared to confer a lower risk of ALS (odds ratio = 0.5, 95% CI: 0.3, 0.8) than loss due to other causes. These data indicate that the risk of developing ALS decreases following the severe stress of parental bereavement. Further studies are needed to explore potential underlying mechanisms.

Role of IRAK4 and IRF3 in the control of intracellular infection with Chlamydia pneumoniae.

TLR signal transduction involves a MyD88-mediated pathway, which leads to recruitment of the IL-1 receptor (IL-1R)-associated kinase 4 (IRAK4) and Toll/IL-1R translation initiation region domain-containing adaptor-inducing IFN-beta-mediated pathway, resulting in the activation of IFN regulatory factor (IRF)3. Both pathways can lead to expression of IFN-beta. TLR-dependent and -independent signals converge in the TNF receptor-associated factor 6 (TRAF6) adaptor, which mediates the activation of NF-kappaBeta. Infection of murine bone marrow-derived macrophages (BMM) with Chlamydia pneumoniae induces IFN-alpha/beta- and NF-kappaBeta-dependent expression of IFN-gamma, which in turn, will control bacterial growth. The role of IRAK4 and IRF3 in the regulation of IFN-alpha/beta expression and NF-kappaBeta activation was studied in C. pneumoniae-infected BMM. We found that levels of IFN-alpha, IFN-beta, and IFN-gamma mRNA were reduced in infected IRAK4(-/-) BMM compared with wild-type (WT) controls. BMM also showed an IRAK4-dependent growth control of C. pneumoniae. No increased IRF3 activation was detected in C. pneumoniae-infected BMM. Similar numbers of intracellular bacteria, IFN-alpha, and IFN-gamma mRNA titers were observed in C. pneumoniae-infected IRF3(-/-) BMM. On the contrary, IFN-beta(-/-) BMM showed lower IFN-alpha and IFN-gamma mRNA levels and higher bacterial titers compared with WT controls. C. pneumoniae infection-induced activation of NF-kappaBeta and expression of proinflammatory cytokines were shown to be TRAF6-dependent but did not require IRAK4 or IRF3. Thus, our data indicate that IRAK4, but not IRF3, controls C. pneumoniae-induced IFN-alpha and IFN-gamma secretion and bacterial growth. IRAK4 and IRF3 are redundant for infection-induced NF-kappaB activation, which is regulated by TRAF6.

The role of IFN-gamma in the outcome of chlamydial infection.

Chlamydia are intracellular bacteria which infect many vertebrates, including humans. They cause a myriad of severe diseases, ranging from asymptomatic infection to pneumonia, blindness or infertility. IFN-gamma plays an important role in defense against acute infection and in the establishment of persistence. Chlamydia have evolved mechanisms to escape IFN-gamma functions. IFN-gamma-mediated effector mechanisms may involve effects on the metabolism of tryptophan or iron, on the inducible NO synthase (iNOS), on the secretion of chemokines and adhesion molecules or on the regulation of T-cell activities. IFN-gamma is secreted by the innate and the adaptive arms of the immune system. Within the former, Chlamydia-infected macrophages express IFN-gamma that in turn mediates resistance to infection. IFN-alpha/beta are pivotal for both IFN-gamma- and iNOS-mediated resistance to chlamydial infection in macrophages.

Ionizing air affects influenza virus infectivity and prevents airborne-transmission.

By the use of a modified ionizer device we describe effective prevention of airborne transmitted influenza A (strain Panama 99) virus infection between animals and inactivation of virus (>97%). Active ionizer prevented 100% (4/4) of guinea pigs from infection. Moreover, the device effectively captured airborne transmitted calicivirus, rotavirus and influenza virus, with recovery rates up to 21% after 40 min in a 19 m(3) room. The ionizer generates negative ions, rendering airborne particles/aerosol droplets negatively charged and electrostatically attracts them to a positively charged collector plate. Trapped viruses are then identified by reverse transcription quantitative real-time PCR. The device enables unique possibilities for rapid and simple removal of virus from air and offers possibilities to simultaneously identify and prevent airborne transmission of viruses.

Phase I/II trial of HIV-1 hyperimmune globulin for the prevention of HIV-1 vertical transmission in Uganda.

OBJECTIVES: To assess the safety, tolerance, pharmacokinetics, and virologic and immunologic changes associated with the use of Ugandan HIV hyperimmune globulin (HIVIGLOB) in HIV infected pregnant Ugandan women and their infants. DESIGN: A prospective, phase I/II, three-arm dose escalation trial of HIVIGLOB. METHODS: HIVIGLOB was prepared from discarded HIV infected units of blood collected from the National Blood Bank in Kampala. From June 1996 to April 1997, 31 HIV positive pregnant women were enrolled with HIVIGLOB infusions given at 37 weeks gestation and within 16 h of birth for infants. The first 10 mother-infant pairs were infused at a dose of 50 mg/kg, followed by 11 pairs at 200 mg/kg, and 10 pairs at 400 mg/kg. Study participants were followed for 30 months. RESULTS: Thirty-one women and 29 infants were infused with HIVIGLOB. The infusions were safe and well tolerated by the women and their infants at all doses. There were no significant changes in virologic or immunologic parameters after HIVIGLOB infusion. Pharmacokinetic properties of this product were similar to other immune globulin products with a median half-life of 28 days in women and 30 days in infants. CONCLUSION: An HIV immune globulin product derived from HIV infected Ugandan donors is safe, well tolerated, and has pharmacokinetic properties consistent with other immunoglobulin products. Data suggest that a 400 mg/kg dose of HIVIGLOB would be the most appropriate dose for a subsequent efficacy trial of HIVIGLOB for the prevention of mother to child HIV transmission.

Micrometer-sized particles in cerebrospinal fluid (CSF) in patients with schizophrenia.

The etiology of schizophrenia is unknown, but the pathogenetic process involves organic changes in brain tissue, which may alter the composition of cerebrospinal fluid (CSF). For the present study, CSF was obtained by lumbar puncture from 22 schizophrenic patients and 38 control patients. We have used scanning electron microscopy combined with filtration techniques to search for pathogenic correlates and diagnostic biomarkers in the nano-micrometer range. Micrometer-sized spherical particles were isolated from CSF in 20 of the 22 patients with schizophrenia compared to only two of the 38 controls (P < 0.001). Reverse transcription-polymerase chain reaction analysis did not reveal bacterial DNA material in the particles. The particles have not replicated in culture. The micrometer-sized particles may serve as biological disease markers in schizophrenia. Hypothetically, they may be involved in development of the disease or may result from the disease process in brains of schizophrenic patients.

Safety and efficacy of HIV hyperimmune globulin for prevention of mother-to-child HIV transmission in HIV-1-infected pregnant women and their infants in Kampala, Uganda (HIVIGLOB/NVP STUDY).

BACKGROUND: This phase III, randomized, clinical trial compared single-dose nevirapine (sdNVP) plus HIV hyperimmune globulin (HIVIGLOB) with sdNVP alone for preventing maternal-to-child transmission of HIV. Primary objectives were to determine rates of HIV infection among infants and to assess the safety of HIVIGLOB in combination with sdNVP in HIV-infected Ugandan pregnant women and their infants. METHODS: Mother-infant pairs were randomized to receive 200 mg of nevirapine to women in labor and 2 mg/kg NVP to newborns within 72 hours after birth (sdNVP arm) or to receive sdNVP plus a single intravenous 240-mL dose of HIVIGLOB given to women at 36- to 38-week gestation and a single intravenous 24-mL dose to newborns within 18 hours of birth (HIVIGLOB/sdNVP arm). Risk of HIV infection was determined using Kaplan-Meier and risk ratio estimates at birth, 2, 6, 14 weeks, 6, and 12 months of age. RESULTS: Intent-to-treat analysis included 198 HIVIGLOB/sdNVP and 294 sdNVP mother-infant pairs. At 6 months of age, the primary endpoint, there was no statistically significant difference in HIV transmission in the HIVIGLOB/sdNVP arm vs. the sdNVP arm [18.7% vs. 15.0%; risk ratio = 1.240 (95% confidence interval: 0.833 to 1.846); P = 0.290]. Similarly, the proportion of serious adverse events in the HIVIGLOB/sdNVP and sdNVP arms, respectively, for mothers (18.9% vs. 19.3%; P = 0.91) and infants (62.6% vs. 59.5%; P = 0.51) was not significantly different. CONCLUSIONS: Giving mother-infant pairs an infusion of peripartum HIV hyperimmune globulin in addition to sdNVP for preventing maternal-to-child transmission was as safe as sdNVP alone but was no more effective than sdNVP alone in preventing HIV transmission.

Feasibility study on the treatment of small breast carcinoma using percutaneous US-guided preferential radiofrequency ablation (PRFA).

The purpose of this study was to determine the safety and efficacy of percutaneous ultrasound (US) guided preferential radiofrequency ablation (PRFA) of unifocal human invasive breast carcinoma with largest radiological diameters of up to 16 mm. Thirty-three patients were enrolled in a study to be treated prior to scheduled partial mastectomy. A needle-shaped treatment electrode, successively developed in two different sizes, was placed into the center of the lesions using ultrasound guidance. A temperature of 85 degrees C was maintained for 10 min. The analysis of the resected specimen was performed using conventional histopathological methods with the aim to determine the size of the lesion as well as the potential viability of tumor cells. Of the 33 patients enrolled 31 were treated. In 26 (84%) patients a complete ablation of the tumor was achieved. Ultrasound guided preferential radiofrequency ablation of small breast carcinoma is feasible and patient friendly. The success rate depends on accurate preoperative diagnostic imaging as well as an exact position of the needle electrode.

Use of non-invasive bioluminescent imaging to assess mycobacterial dissemination in mice, treatment with bactericidal drugs and protective immunity.

Monitoring the spread of mycobacterium in vivo using biophotonic imaging provides a fast, reliable and sensitive method to evaluate the distribution of the infection. Moreover, this technique allows for a significant reduction in the number of animals required in comparison to conventional anatomopathological studies. Here, we describe for the first time and validate the use of a luciferase-tagged recombinant Mycobacterium bovis BCG for non-invasive bioluminescent imaging of 1) bacterial dissemination in tissues, 2) the efficacy of treatment with anti-mycobacterial drugs and 3) the role of adaptive immune responses in controlling mycobacterial infection in vivo.

Preclinical assessment of the treatment of second-stage African trypanosomiasis with cordycepin and deoxycoformycin.

BACKGROUND: There is an urgent need to substitute the highly toxic compounds still in use for treatment of the encephalitic stage of human African trypanosomiasis (HAT). We here assessed the treatment with the doublet cordycepin and the deaminase inhibitor deoxycoformycin for this stage of infection with Trypanosoma brucei (T.b.). METHODOLOGY/PRINCIPAL FINDINGS: Cordycepin was selected as the most efficient drug from a direct parasite viability screening of a compound library of nucleoside analogues. The minimal number of doses and concentrations of the drugs effective for treatment of T.b. brucei infections in mice were determined. Oral, intraperitoneal or subcutaneous administrations of the compounds were successful for treatment. The doublet was effective for treatment of late stage experimental infections with human pathogenic T.b. rhodesiense and T.b. gambiense isolates. Late stage infection treatment diminished the levels of inflammatory cytokines in brains of infected mice. Incubation with cordycepin resulted in programmed cell death followed by secondary necrosis of the parasites. T.b. brucei strains developed resistance to cordycepin after culture with increasing concentrations of the compound. However, cordycepin-resistant parasites showed diminished virulence and were not cross-resistant to other drugs used for treatment of HAT, i.e. pentamidine, suramin and melarsoprol. Although resistant parasites were mutated in the gene coding for P2 nucleoside adenosine transporter, P2 knockout trypanosomes showed no altered resistance to cordycepin, indicating that absence of the P2 transporter is not sufficient to render the trypanosomes resistant to the drug. CONCLUSIONS/SIGNIFICANCE: Altogether, our data strongly support testing of treatment with a combination of cordycepin and deoxycoformycin as an alternative for treatment of second-stage and/or melarsoprol-resistant HAT.

SOCS-1 protects against Chlamydia pneumoniae-induced lethal inflammation but hampers effective bacterial clearance.

Suppressor of cytokine signaling 1 (SOCS1) plays a major role in the inhibition of STAT1-mediated responses. STAT1-dependent responses are critical for resistance against infection with Chlamydia pneumoniae. We studied the regulation of expression of SOCS1 and SOCS3, and the role of SOCS1 during infection with C. pneumoniae in mice. Bone marrow-derived macrophages (BMM) and dendritic cells in vitro or lungs in vivo all showed enhanced STAT1-dependent SOCS1 mRNA accumulation after infection with C. pneumoniae. Infection-increased SOCS1 mRNA levels were dependent on IFN-alphabeta but not on IFN-gamma. T or B cells were not required for SOCS1 mRNA accumulation in vivo. Infection-induced STAT1-phosphorylation occurred more rapidly in SOCS1(-/-) BMM. In agreement, expression of IFN-gamma responsive genes, but not IL-1beta, IL-6, or TNF-alpha were relatively increased in C. pneumoniae-infected SOCS1(-/-) BMM. Surprisingly, C. pneumoniae infection-induced IFN-alpha, IFN-beta, and IFN-gamma expression in BMM were attenuated by SOCS1. C. pneumoniae infection of RAG1(-/-)/SOCS1(-/-) mice induced a rapid lethal inflammation, accompanied by diminished pulmonary bacterial load and increased levels of iNOS and IDO but not IL-1beta, IL-6, or TNF-alpha mRNA. In summary, C. pneumoniae infection induces a STAT1, IFN-alphabeta-dependent and IFN-gamma independent SOCS1 mRNA accumulation. Presence of SOCS1 controls the infection-induced lethal inflammatory disease but impairs the bacterial control.

STAT1 regulates IFN-alpha beta- and IFN-gamma-dependent control of infection with Chlamydia pneumoniae by nonhemopoietic cells.

STAT1 mediates signaling in response to IFN-alpha, -beta, and -gamma, cytokines required for protective immunity against several viral, bacterial, and eukaryotic pathogens. The protective role of STAT1 in the control of intranasal infection with the obligate intracellular bacterium Chlamydia pneumoniae was analyzed. IFN-gamma-/- or IFN-gamma receptor (R)-/- mice were highly susceptible to infection with C. pneumoniae. We found that STAT1-/- mice were even more susceptible to C. pneumoniae than IFN-gamma-/- or IFN-gammaR-/- mice. Phosphorylation of STAT1 was detected in the lungs of C. pneumoniae-infected wild-type, IFN-gammaR-/-, and IFN-alphabetaR-/- mice, but not in mice lacking both IFN-alphabetaR and IFN-gammaR. In line with this, IFN-alphabetaR-/-/IFN-gammaR-/- mice showed increased susceptibility to infection compared with IFN-gammaR-/- mice. However, C. pneumoniae-infected IFN-alphabetaR-/- or IFN regulatory factor 3-/- mice showed no increased susceptibility and similar IFN-gamma expression compared with wild-type mice. CD4+ or CD8+ cells released IFN-gamma in vivo and conferred protection against C. pneumoniae in a STAT1-independent manner. In contrast, STAT1 mediated a nonredundant protective role of nonhemopoietic cells but not of hemopoietic cells. Nonhemopoietic cells accounted for the expression of STAT1-mediated indoleamine 2, 3-dioxygenase and the p47 GTPase LRG-47, but not inducible NO synthase mRNA. In summary, we demonstrate that STAT1 mediates a cooperative effect of IFN-alphabeta and IFN-gamma on nonhemopoietic cells, resulting in protection against C. pneumoniae.

Treatment of African trypanosomiasis with cordycepin and adenosine deaminase inhibitors in a mouse model.

There is an urgent need to discontinue the use of highly toxic compounds still in use for treatment of the encephalitic stage of human African trypanosomiasis (HAT). We show here that intraperitoneal injection of the adenosine analogue cordycepin (3'-deoxyadenosine), together with an adenosine deaminase (ADA) inhibitor (coformycin or deoxycoformycin), cures Trypanosoma brucei brucei infection in mice. Treatment was also effective at a stage when the trypanosomes had penetrated into the brain parenchyma, as determined by double immunolabeling of parasites and cerebral vessel endothelial cells in brain sections. At this stage, the parasites were eliminated not only from the blood but also from the brain parenchyma. In parallel with the elimination of parasites, in treated mice, the number of CD45+ inflammatory cells in the brain parenchyma was reduced. Treatment was not immunosuppressive. In vitro incubation with cordycepin reduced the growth of T. brucei brucei and T. cruzi, as well as Leishmania major and L. amazonensis. Administration of cordycepin plus deoxycofomycin to T. cruzi-infected mice also significantly reduced parasitemia. Accordingly, we propose nucleoside analogues resistant to ADA as candidates for treatment of late-stage HAT.

Macrophages, CD4+ or CD8+ cells are each sufficient for protection against Chlamydia pneumoniae infection through their ability to secrete IFN-gamma.

By using a T, B, or NK cell-deficient mouse strain (recombinase-activating gene (RAG)-1(-/-)/common cytokine receptor gamma-chain (gamma(C)R)), and T and B cell and IFN-gamma-deficient (RAG-1(-/-)/IFN-gamma(-/-)) mice, we have studied the generation of immunity against infection by Chlamydia pneumoniae. We found that IFN-gamma secreted by innate-cell populations protect against C. pneumoniae infection. However, NK cells were not needed for such IFN-gamma-dependent innate immune protection. Inoculation of wild type, but not IFN-gamma(-/-) bone marrow-derived macrophages protected RAG-1(-/-)/IFN-gamma(-/-) mice against C. pneumoniae infection. In line, pulmonary macrophages from RAG-1(-/-) C. pneumoniae-infected mice expressed IFN-gamma mRNA. Reconstitution of RAG-1(-/-)/gamma(c)R(-/-) or RAG-1(-/-)/IFN-gamma(-/-) mice with CD4(+) or CD8(+) cells by i.v. transfer of FACS sorted wild type spleen cells (SC) increased resistance to C. pneumoniae infection. On the contrary, no protection was observed upon transfer of IFN-gamma(-/-) CD4(+) or IFN-gamma(-/-) CD8(+) SC. T cell-dependent protection against C. pneumoniae was weaker when IFN-gammaR(-/-) CD4(+) or IFN-gammaR(-/-) CD8(+) SC were inoculated into RAG-1(-/-)/IFN-gamma(-/-) mice. Thus both nonlymphoid and T cell-derived IFN-gamma can play a central and complementary role in protection against C. pneumoniae. IFN-gamma secreted by nonlymphoid cells was not required for T cell-mediated protection against C. pneumoniae; however, IFN-gamma regulated T cell protective functions.

Leukemia-associated monoclonal and oligoclonal TCR-BV use in patients with B-cell chronic lymphocytic leukemia.

T-cell receptor-B-variable (TCR-BV) gene usage and the CDR3 size distribution pattern were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) in patients with B-cell chronic lymphocytic leukemia (B-CLL) to assess the T-cell repertoire. The use of TCR-BV families in CD4 and CD8 T cells stimulated with autologous activated leukemic cells was compared with that of freshly obtained blood T cells. Overexpression of individual TCR-BV families was found in freshly isolated CD4 and CD8 T cells. Polyclonal, oligoclonal, and monoclonal TCR-CDR3 patterns were seen within such overexpressed native CD4 and CD8 TCR-BV families. In nonoverexpressed TCR-BV families, monoclonal and oligoclonal populations were noted only within the CD8 subset. After in vitro stimulation of T cells with autologous leukemic B cells, analyses of the CDR3 length patterns showed that in expanded TCR-BV populations, polyclonal patterns frequently shifted toward a monoclonal/oligoclonal profile, whereas largely monoclonal patterns in native overexpressed TCR-BV subsets remained monoclonal. Seventy-five percent of CD8 expansions found in freshly obtained CD8 T cells further expanded on in vitro stimulation with autologous leukemic B cells. This suggests a memory status of such cells. In contrast, the unusually high frequency of CD4 T-cell expansions found in freshly isolated peripheral blood cells did not correlate positively to in vitro stimulation as only 1 of 9 expansions continued to expand. Our data suggest that leukemia cell-specific memory CD4 and CD8 T cells are present in vivo of patients with CLL and that several leukemia cell-associated antigens/epitopes are recognized by the patients' immune system, indicating that whole leukemia cells might be of preference for vaccine development.