Antibody Lineages with Vaccine-Induced Antigen-Binding Hotspots Develop Broad HIV Neutralization.

The vaccine-mediated elicitation of antibodies (Abs) capable of neutralizing diverse HIV-1 strains has been a long-standing goal. To understand how broadly neutralizing antibodies (bNAbs) can be elicited, we identified, characterized, and tracked five neutralizing Ab lineages targeting the HIV-1-fusion peptide (FP) in vaccinated macaques over time. Genetic and structural analyses revealed two of these lineages to belong to a reproducible class capable of neutralizing up to 59% of 208 diverse viral strains. B cell analysis indicated each of the five lineages to have been initiated and expanded by FP-carrier priming, with envelope (Env)-trimer boosts inducing cross-reactive neutralization. These Abs had binding-energy hotspots focused on FP, whereas several FP-directed Abs induced by immunization with Env trimer-only were less FP-focused and less broadly neutralizing. Priming with a conserved subregion, such as FP, can thus induce Abs with binding-energy hotspots coincident with the target subregion and capable of broad neutralization.

Maturation Pathway from Germline to Broad HIV-1 Neutralizer of a CD4-Mimic Antibody.

Antibodies with ontogenies from VH1-2 or VH1-46-germline genes dominate the broadly neutralizing response against the CD4-binding site (CD4bs) on HIV-1. Here, we define with longitudinal sampling from time-of-infection the development of a VH1-46-derived antibody lineage that matured to neutralize 90% of HIV-1 isolates. Structures of lineage antibodies CH235 (week 41 from time-of-infection, 18% breadth), CH235.9 (week 152, 77%), and CH235.12 (week 323, 90%) demonstrated the maturing epitope to focus on the conformationally invariant portion of the CD4bs. Similarities between CH235 lineage and five unrelated CD4bs lineages in epitope focusing, length-of-time to develop breadth, and extraordinary level of somatic hypermutation suggested commonalities in maturation among all CD4bs antibodies. Fortunately, the required CH235-lineage hypermutation appeared substantially guided by the intrinsic mutability of the VH1-46 gene, which closely resembled VH1-2. We integrated our CH235-lineage findings with a second broadly neutralizing lineage and HIV-1 co-evolution to suggest a vaccination strategy for inducing both lineages.

Longitudinal Analysis Reveals Early Development of Three MPER-Directed Neutralizing Antibody Lineages from an HIV-1-Infected Individual.

Lineage-based vaccine design is an attractive approach for eliciting broadly neutralizing antibodies (bNAbs) against HIV-1. However, most bNAb lineages studied to date have features indicative of unusual recombination and/or development. From an individual in the prospective RV217 cohort, we identified three lineages of bNAbs targeting the membrane-proximal external region (MPER) of the HIV-1 envelope. Antibodies RV217-VRC42.01, -VRC43.01, and -VRC46.01 used distinct modes of recognition and neutralized 96%, 62%, and 30%, respectively, of a 208-strain virus panel. All three lineages had modest levels of somatic hypermutation and normal antibody-loop lengths and were initiated by the founder virus MPER. The broadest lineage, VRC42, was similar to the known bNAb 4E10. A multimeric immunogen based on the founder MPER activated B cells bearing the unmutated common ancestor of VRC42, with modest maturation of early VRC42 intermediates imparting neutralization breadth. These features suggest that VRC42 may be a promising template for lineage-based vaccine design.

A potent and broad neutralization of SARS-CoV-2 variants of concern by DARPins.

We report the engineering and selection of two synthetic proteins-FSR16m and FSR22-for the possible treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. FSR16m and FSR22 are trimeric proteins composed of DARPin SR16m or SR22 fused with a T4 foldon. Despite selection by a spike protein from a now historical SARS-CoV-2 strain, FSR16m and FSR22 exhibit broad-spectrum neutralization of SARS-CoV-2 strains, inhibiting authentic B.1.351, B.1.617.2 and BA.1.1 viruses, with respective IC50 values of 3.4, 2.2 and 7.4 ng ml-1 for FSR16m. Cryo-EM structures revealed that these DARPins recognize a region of the receptor-binding domain (residues 456, 475, 486, 487 and 489) overlapping a critical portion of the angiotensin-converting enzyme 2 (ACE2)-binding surface. K18-hACE2 transgenic mice inoculated with B.1.617.2 and receiving intranasally administered FSR16m showed less weight loss and 10-100-fold lower viral burden in upper and lower respiratory tracts. The strong and broad neutralization potency makes FSR16m and FSR22 promising candidates for the prevention and treatment of infection by SARS-CoV-2.

Antiviral Activity and Crystal Structures of HIV-1 gp120 Antagonists.

As part of our effort to discover drugs that target HIV-1 entry, we report the antiviral activity and crystal structures of two novel inhibitors in a complex with a gp120 core. NBD-14204 showed similar antiviral activity against all the clinical isolates tested. The IC50 values were in the range of 0.24-0.9 µM with an overall mean of 0.47 ± 0.03 µM, showing slightly better activity against the clinical isolates than against the lab-adapted HIV-1HXB2 (IC50 = 0.96 ± 0.1 µM). Moreover, the antiviral activity of NBD-14208 was less consistent, showing a wider range of IC50 values (0.66-5.7 µM) with an overall mean of 3 ± 0.25 µM and better activity against subtypes B and D (Mean IC50 2.2-2.5 µM) than the A, C and Rec viruses (Mean IC50 2.9-3.9 µM). SI of NBD-14204 was about 10-fold higher than NBD-14208, making it a better lead compound for further optimization. In addition, we tested these compounds against S375Y and S375H mutants of gp120, which occurred in some clades and observed these to be sensitive to NBD-14204 and NBD-14208. These inhibitors also showed modest activity against HIV-1 reverse transcriptase. Furthermore, we determined the crystal structures of both inhibitors in complexes with gp120 cores. As expected, both NBD-14204 and NBD-14208 bind primarily within the Phe43 cavity. It is noteworthy that the electron density of the thiazole ring in both structures was poorly defined due to the flexibility of this scaffold, suggesting that these compounds maintain substantial entropy, even when bound to the Phe43 cavity.

Optimization of the Solubility of HIV-1-Neutralizing Antibody 10E8 through Somatic Variation and Structure-Based Design.

UNLABELLED: Extraordinary antibodies capable of near pan-neutralization of HIV-1 have been identified. One of the broadest is antibody 10E8, which recognizes the membrane-proximal external region (MPER) of the HIV-1 envelope and neutralizes >95% of circulating HIV-1 strains. If delivered passively, 10E8 might serve to prevent or treat HIV-1 infection. Antibody 10E8, however, is markedly less soluble than other antibodies. Here, we describe the use of both structural biology and somatic variation to develop optimized versions of 10E8 with increased solubility. From the structure of 10E8, we identified a prominent hydrophobic patch; reversion of four hydrophobic residues in this patch to their hydrophilic germ line counterparts resulted in an ∼10-fold decrease in turbidity. We also used somatic variants of 10E8, identified previously by next-generation sequencing, to optimize heavy and light chains; this process yielded several improved variants. Of these, variant 10E8v4 with 26 changes versus the parent 10E8 was the most soluble, with a paratope we showed crystallographically to be virtually identical to that of 10E8, a potency on a panel of 200 HIV-1 isolates also similar to that of 10E8, and a half-life in rhesus macaques of ∼10 days. An anomaly in 10E8v4 size exclusion chromatography that appeared to be related to conformational isomerization was resolved by engineering an interchain disulfide. Thus, by combining a structure-based approach with natural variation in potency and solubility from the 10E8 lineage, we successfully created variants of 10E8 which retained the potency and extraordinary neutralization breadth of the parent 10E8 but with substantially increased solubility. IMPORTANCE: Antibody 10E8 could be used to prevent HIV-1 infection, if manufactured and delivered economically. It suffers, however, from issues of solubility, which impede manufacturing. We hypothesized that the physical characteristic of 10E8 could be improved through rational design, without compromising breadth and potency. We used structural biology to identify hydrophobic patches on 10E8, which did not appear to be involved in 10E8 function. Reversion of hydrophobic residues in these patches to their hydrophilic germ line counterparts increased solubility. Next, clues from somatic variants of 10E8, identified by next-generation sequencing, were incorporated. A combination of structure-based design and somatic variant optimization led to 10E8v4, with substantially improved solubility and similar potency compared to the parent 10E8. The cocrystal structure of antibody 10E8v4 with its HIV-1 epitope was highly similar to that with the parent 10E8, despite 26 alterations in sequence and substantially improved solubility. Antibody 10E8v4 may be suitable for manufacturing.

Phase 1 trial evaluating safety and pharmacokinetics of HIV-1 broadly neutralizing mAbs 10E8VLS and VRC07-523LS.

BACKGROUNDBroadly neutralizing monoclonal antibodies (bNAbs) represent a promising strategy for HIV-1 immunoprophylaxis and treatment. 10E8VLS and VRC07-523LS are bNAbs that target the highly conserved membrane-proximal external region (MPER) and the CD4-binding site of the HIV-1 viral envelope glycoprotein, respectively.METHODSIn this phase 1, open-label trial, we evaluated the safety and pharmacokinetics of 5 mg/kg 10E8VLS administered alone, or concurrently with 5 mg/kg VRC07-523LS, via s.c. injection to healthy non-HIV-infected individuals.RESULTSEight participants received either 10E8VLS alone (n = 6) or 10E8VLS and VRC07-523LS in combination (n = 2). Five (n = 5 of 8, 62.5%) participants who received 10E8VLS experienced moderate local reactogenicity, and 1 participant (n = 1/8, 12.5%) experienced severe local reactogenicity. Further trial enrollment was stopped, and no participant received repeat dosing. All local reactogenicity resolved without sequelae. 10E8VLS retained its neutralizing capacity, and no functional anti-drug antibodies were detected; however, a serum t1/2 of 8.1 days was shorter than expected. Therefore, the trial was voluntarily stopped per sponsor decision (Vaccine Research Center, National Institute of Allergy and Infectious Diseases [NIAID], NIH). Mechanistic studies performed to investigate the underlying reason for the reactogenicity suggest that multiple mechanisms may have contributed, including antibody aggregation and upregulation of local inflammatory markers.CONCLUSION10E8VLS resulted in unexpected reactogenicity and a shorter t1/2 in comparison with previously tested bNAbs. These studies may facilitate identification of nonreactogenic second-generation MPER-targeting bNAbs, which could be an effective strategy for HIV-1 immunoprophylaxis and treatment.TRIAL REGISTRATIONClinicaltrials.gov, accession no. NCT03565315.FUNDINGDivision of Intramural Research, National Institute of Allergy and Infectious Diseases, NIH.

Improved pharmacokinetics of HIV-neutralizing VRC01-class antibodies achieved by reduction of net positive charge on variable domain.

The amino-acid composition of the immunoglobulin variable region has been observed to impact antibody pharmacokinetics (PK). Here, we sought to improve the PK of the broad HIV-1-neutralizing VRC01-class antibodies, VRC07-523LS and N6LS, by reducing the net positive charge in their variable domains. We used a structure-guided approach to generate a panel of antibody variants incorporating select Arg or Lys substituted to Asp, Gln, Glu, or Ser. The engineered variants exhibited reduced affinity to heparin, reduced polyreactivity, and improved PK in human FcRn-transgenic mice. One variant, VRC07-523LS.v34, with three charge substitutions, had an observed in vivo half-life and an estimated human half-life of 10.8 and 60 days, respectively (versus 5.4 and 38 days for VRC07-523LS) and retained functionality, neutralizing 92% of a 208-strain panel at a geometric mean IC80 <1 µg/mL. Another variant, N6LS.C49, with two charge substitutions, had an observed in vivo half-life and an estimated human half-life of 14.5 and 80 days (versus 9.0 and 44 days for N6LS) and neutralized ~80% of 208 strains at a geometric mean IC80 <1 µg/mL. Since Arg and Lys residues are prevalent in human antibodies, we propose substitution of select Arg or Lys with Asp, Gln, Glu, or Ser in the framework region as a general means to improve PK of therapeutic antibodies.

Trapping the HIV-1 V3 loop in a helical conformation enables broad neutralization.

The third variable (V3) loop on the human immunodeficiency virus 1 (HIV-1) envelope glycoprotein trimer is indispensable for virus cell entry. Conformational masking of V3 within the trimer allows efficient neutralization via V3 only by rare, broadly neutralizing glycan-dependent antibodies targeting the closed prefusion trimer but not by abundant antibodies that access the V3 crown on open trimers after CD4 attachment. Here, we report on a distinct category of V3-specific inhibitors based on designed ankyrin repeat protein (DARPin) technology that reinstitute the CD4-bound state as a key neutralization target with up to >90% breadth. Broadly neutralizing DARPins (bnDs) bound V3 solely on open envelope and recognized a four-turn amphipathic α-helix in the carboxy-terminal half of V3 (amino acids 314-324), which we termed 'αV3C'. The bnD contact surface on αV3C was as conserved as the CD4 binding site. Molecular dynamics and escape mutation analyses underscored the functional relevance of αV3C, highlighting the potential of αV3C-based inhibitors and, more generally, of postattachment inhibition of HIV-1.

Bispecific antibody CAP256.J3LS targets V2-apex and CD4-binding sites with high breadth and potency.

Antibody CAP256-VRC26.25 targets the second hypervariable region (V2) at the apex of the HIV envelope (Env) trimer with extraordinary neutralization potency, although less than optimal breadth. To improve breadth, we linked the light chain of CAP256V2LS, an optimized version of CAP256-VRC26.25 currently under clinical evaluation, to the llama nanobody J3, which has broad CD4-binding site-directed neutralization. The J3-linked bispecific antibody exhibited improved breadth and potency over both J3 and CAP256V2LS, indicative of synergistic neutralization. The cryo-EM structure of the bispecific antibody in complex with a prefusion-closed Env trimer revealed simultaneous binding of J3 and CAP256V2LS. We further optimized the pharmacokinetics of the bispecific antibody by reducing the net positive charge of J3. The optimized bispecific antibody, which we named CAP256.J3LS, had a half-life similar to CAP256V2LS in human FcRn knock-in mice and exhibited suitable auto-reactivity, manufacturability, and biophysical risk. CAP256.J3LS neutralized over 97% of a multiclade 208-strain panel (geometric mean concentration for 80% inhibition (IC80) 0.079 µg/ml) and 100% of a 100-virus clade C panel (geometric mean IC80 of 0.05 µg/ml), suggesting its anti-HIV utility especially in regions where clade C dominates.

Structural basis for llama nanobody recognition and neutralization of HIV-1 at the CD4-binding site.

Nanobodies can achieve remarkable neutralization of genetically diverse pathogens, including HIV-1. To gain insight into their recognition, we determined crystal structures of four llama nanobodies (J3, A12, C8, and D7), all of which targeted the CD4-binding site, in complex with the HIV-1 envelope (Env) gp120 core, and determined a cryoelectron microscopy (cryo-EM) structure of J3 with the Env trimer. Crystal and cryo-EM structures of J3 complexes revealed this nanobody to mimic binding to the prefusion-closed trimer for the primary site of CD4 recognition as well as a secondary quaternary site. In contrast, crystal structures of A12, C8, and D7 with gp120 revealed epitopes that included portions of the gp120 inner domain, inaccessible on the prefusion-closed trimer. Overall, these structures explain the broad and potent neutralization of J3 and limited neutralization of A12, C8, and D7, which utilized binding modes incompatible with the neutralization-targeted prefusion-closed conformation of Env.

A matrix of structure-based designs yields improved VRC01-class antibodies for HIV-1 therapy and prevention.

Passive transfer of broadly neutralizing antibodies is showing promise in the treatment and prevention of HIV-1. One class of antibodies, the VRC01 class, appears especially promising. To improve VRC01-class antibodies, we combined structure-based design with a matrix-based approach to generate VRC01-class variants that filled an interfacial cavity, used diverse third-complementarity-determining regions, reduced potential steric clashes, or exploited extended contacts to a neighboring protomer within the envelope trimer. On a 208-strain panel, variant VRC01.23LS neutralized 90% of the panel at a geometric mean IC80 less than 1 µg/ml, and in transgenic mice with human neonatal-Fc receptor, the serum half-life of VRC01.23LS was indistinguishable from that of the parent VRC01LS, which has a half-life of 71 d in humans. A cryo-electron microscopy structure of VRC01.23 Fab in complex with BG505 DS-SOSIP.664 Env trimer determined at 3.4-Å resolution confirmed the structural basis for its ~10-fold improved potency relative to VRC01. Another variant, VRC07-523-F54-LS.v3, neutralized 95% of the 208-isolated panel at a geometric mean IC80 of less than 1 µg/ml, with a half-life comparable to that of the parental VRC07-523LS. Our matrix-based structural approach thus enables the engineering of VRC01 variants for HIV-1 therapy and prevention with improved potency, breadth, and pharmacokinetics.

Prognostic significance of Notch 3 gene expression in ovarian serous carcinoma.

The Notch signaling pathway is an important cell signaling system, which regulates cell differentiation, proliferation, and apoptosis, and is aberrantly activated in a wide range of cancer, including ovarian cancers. However, it remains unclear as to whether Notch signaling plays a role in the progression and prognosis of ovarian cancer. We examined the mRNA and protein expression of Notch 3, Jagged 1, and Jagged 2 in 98 ovarian epithelial tumors via real-time PCR and in 175 tumors with immunohistochemical analysis, and then correlated their expression levels with clinicopathological parameters and patient survival. In this study, we detected high levels of Notch3 mRNA and protein expression especially in serous ovarian carcinomas compared to their benign counterparts, accompanied by a positive correlation with the expressions of Jagged 1 and Jagged 2. High levels of Notch 3 mRNA expression (>2-fold than that of benign tumor) were noted in 63% of the serous carcinomas (mean level: 17-fold, P = 0.032). Additionally, Notch 3 protein overexpression was significantly associated with advanced stage (P = 0.0008), lymph node (P = 0.001), and distant metastasis (P = 0.003). Notably, high Notch 3 mRNA and protein expressions were correlated with chemoresistance (P = 0.033) and poor overall survival (P = 0.027, P = 0.042) in these patients. Our results indicate that the Notch 3 signaling pathway is involved in the tumor progression of ovarian serous carcinoma, and higher Notch 3 expression may be an independent poor prognostic factor in this subset of tumors.

HIV-1 Envelope and MPER Antibody Structures in Lipid Assemblies.

Structural and functional studies of HIV envelope glycoprotein (Env) as a transmembrane protein have long been complicated by challenges associated with inherent flexibility of the molecule and the membrane-embedded hydrophobic regions. Here, we present approaches for incorporating full-length, wild-type HIV-1 Env, as well as C-terminally truncated and stabilized versions, into lipid assemblies, providing a modular platform for Env structural studies by single particle electron microscopy. We reconstitute a full-length Env clone into a nanodisc, complex it with a membrane-proximal external region (MPER) targeting antibody 10E8, and structurally define the full quaternary epitope of 10E8 consisting of lipid, MPER, and ectodomain contacts. By aligning this and other Env-MPER antibody complex reconstructions with the lipid bilayer, we observe evidence of Env tilting as part of the neutralization mechanism for MPER-targeting antibodies. We also adapt the platform toward vaccine design purposes by introducing stabilizing mutations that allow purification of unliganded Env with a peptidisc scaffold.

Safety and pharmacokinetics of broadly neutralising human monoclonal antibody VRC07-523LS in healthy adults: a phase 1 dose-escalation clinical trial.

BACKGROUND: Human monoclonal antibodies that potently and broadly neutralise HIV-1 are under development to prevent and treat HIV-1 infection. In this phase 1 clinical trial we aimed to determine the safety, tolerability, and pharmacokinetic profile of the broadly neutralising monoclonal antibody VRC07-523LS, an engineered variant of VRC01 that targets the CD4 binding site of the HIV-1 envelope protein. METHODS: This phase 1, open-label, dose-escalation clinical trial was done at the National Institutes of Health Clinical Center in Bethesda, MD, USA. Individuals were recruited from the greater Washington, DC, area by IRB-approved written and electronic media. We enrolled healthy, HIV-1-negative adults aged 18-50 years. Inclusion criteria were good general health, measured through clinical laboratory tests, medical history, and physical examination. Participants self-selected into one of seven open groups during enrolment without randomisation. Four groups received a single intravenous dose of 1, 5, 20, or 40 mg/kg of VRC07-523LS, and one group received a single 5 mg/kg subcutaneous dose. Two groups received three doses of either 20 mg/kg intravenous VRC07-523LS, or 5 mg/kg subcutaneous VRC07-523LS at 12-week intervals. The primary outcome was the safety and tolerability of VRC07-523LS, assessed by dose, route, and number of administrations. This study is registered with ClinicalTrials.gov, NCT03015181. FINDINGS: Between Feb 21, 2017, and September 13, 2017, we enrolled 26 participants, including 11 (42%) men and 15 (58%) women. Two (8%) participants withdrew from the study early: one participant in group 1 enrolled in the study but never received VRC07-523LS, and one participant in group 6 chose to withdraw after a single administration. One (4%) participant in group 7 received only one of the three scheduled administrations. 17 participants received intravenous administrations and 8 participants received subcutaneous administrations. VRC07-523LS was safe and well tolerated, we observed no serious adverse events or dose-limiting toxic effects. All reported local and systemic reactogenicity was mild to moderate in severity. The most commonly reported symptoms following intravenous administration were malaise or myalgia in three (18%) participants and headache or chills in two (12%) participants. The most commonly reported symptoms following subcutaneous administration were pain and tenderness in four participants (50%) and malaise or headache in three (38%) participants. INTERPRETATION: Safe and well tolerated, VRC07-523LS is a strong and practical candidate for inclusion in HIV-1 prevention and therapeutic strategies. The results from this trial also indicate that an HIV-1 broadly neutralising monoclonal antibody engineered for improved pharmacokinetic and neutralisation properties can be safe for clinical use. FUNDING: National Institutes of Health.

Surface-Matrix Screening Identifies Semi-specific Interactions that Improve Potency of a Near Pan-reactive HIV-1-Neutralizing Antibody.

Highly effective HIV-1-neutralizing antibodies could have utility in the prevention or treatment of HIV-1 infection. To improve the potency of 10E8, an antibody capable of near pan-HIV-1 neutralization, we engineered 10E8-surface mutants and screened for improved neutralization. Variants with the largest functional enhancements involved the addition of hydrophobic or positively charged residues, which were positioned to interact with viral membrane lipids or viral glycan-sialic acids, respectively. In both cases, the site of improvement was spatially separated from the region of antibody mediating molecular contact with the protein component of the antigen, thereby improving peripheral semi-specific interactions while maintaining unmodified dominant contacts responsible for broad recognition. The optimized 10E8 antibody, with mutations to phenylalanine and arginine, retained the extraordinary breadth of 10E8 but with ∼10-fold increased potency. We propose surface-matrix screening as a general method to improve antibodies, with improved semi-specific interactions between antibody and antigen enabling increased potency without compromising breadth.

Epitope-based vaccine design yields fusion peptide-directed antibodies that neutralize diverse strains of HIV-1.

A central goal of HIV-1 vaccine research is the elicitation of antibodies capable of neutralizing diverse primary isolates of HIV-1. Here we show that focusing the immune response to exposed N-terminal residues of the fusion peptide, a critical component of the viral entry machinery and the epitope of antibodies elicited by HIV-1 infection, through immunization with fusion peptide-coupled carriers and prefusion stabilized envelope trimers, induces cross-clade neutralizing responses. In mice, these immunogens elicited monoclonal antibodies capable of neutralizing up to 31% of a cross-clade panel of 208 HIV-1 strains. Crystal and cryoelectron microscopy structures of these antibodies revealed fusion peptide conformational diversity as a molecular explanation for the cross-clade neutralization. Immunization of guinea pigs and rhesus macaques induced similarly broad fusion peptide-directed neutralizing responses, suggesting translatability. The N terminus of the HIV-1 fusion peptide is thus a promising target of vaccine efforts aimed at eliciting broadly neutralizing antibodies.

The use of green fluorescence gene (GFP)-modified rabbit mesenchymal stem cells (rMSCs) co-cultured with chondrocytes in hydrogel constructs to reveal the chondrogenesis of MSCs.

This study was conducted to reveal the chondrogenesis of mesenchymal stem cells that had been genetically modified with the green fluorescence protein (GFP) gene and then co-cultured with chondrocytes in vitro and in vivo. Subsequent mixing of chondrocytes in the hydrogel constructs induced increased chondrogenic differentiation of the transfected hMSCs. The proliferation and differentiation of MSCs that were transfected with the GFP gene and co-cultured with chondrocytes (1:1 and 1:3) or chondrocytes alone were evaluated by a live/dead assay, MTT assay, GAG & DNA assay, RT-PCR, real time-PCR, and histological and immunochemical analysis in vitro and in vivo. Real-time PCR revealed that the expression of aggrecan and COMP by genetically modified hMSCs co-cultured with chondrocytes was 2 or 3 times greater than that of genetically modified MSCs alone. Moreover, the expression of collagen type II was more than 3.5 times greater than that of genetically modified MSCs alone. 3-D hydrogel constructs co-cultured with chondrocytes and genetically modified MSCs showed a significantly higher number of specific lacunae phenotypes at the end of the 4 week study, regardless of whether they were co-cultured in the presence of chondrocytes. These findings indicate that co-culture with chondrocytes and genetically modified MSCs can be used to engineer well designed implants for the formation of neocartilage by transplanted genetically modified MSCs.