Recency is an important dimension of relevance for real-time Twitter search as users tend to be interested in fresh news and events. By incorporating various sources of evidence, the application of learning to rank (LTR) algorithms to real-time Twitter search has shown beneficial in finding not only relevant, but also recent tweets in response to given queries. However, the potential effectiveness brought by LTR may not have been fully exploited due to the lack of labeled data available for properly learning a ranking model, since human labels are expensive in real-world applications. To this end, this paper proposes a transductive algorithm that incrementally aggregate the labeled tweets through an iterative process. Experimental results on the standard Tweets11 dataset show that our approach is able to outperform strong baselines without the use of human labels.